“Again you have heard that it was said to those of old, ‘You shall not swear falsely, but shall perform to the Lord what you have sworn.’ But I say to you, do not take an oath at all, either by heaven, for it is the throne of God, or by the earth, for it is His footstool, or by Jerusalem, for it is the city of the great King. And do not take an oath by your head, for you cannot make one hair white or black. Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil.”
– Matthew 5:33-37
“But above all, my brothers, do not swear, either by heaven or by earth or by any other oath, but let your “yes” be yes and your “no” be no, so that you may not fall under condemnation.”
– James 5:12
“For God is my witness…that without ceasing I mention you always in my prayers.”
– Romans 1:9-10
“The God and Father of the Lord Jesus, he who is blessed forever, knows that I am not lying.”
– 1 Corinthians 11:31
“But I call God to witness against me—it was to spare you that I refrained from coming again to Corinth.”
– 2 Corinthians 1:23
“In what I am writing to you, before God, I do not lie!”
– Galatians 1:20
“For God is my witness, how I yearn for you all with the affection of Christ Jesus.”
– Philippians 1:8
“And the high priest said to him, “I adjure you by the living God, tell us if you are the Christ, the Son of God.” Jesus said to him, “You have said so. But I tell you, from now on you will see the Son of Man seated at the right hand of Power and coming on the clouds of heaven.””
– Matthew 26:63-64
“For when God made a promise to Abraham, since he had no one greater by whom to swear, he swore by himself, saying, “Surely I will bless you and multiply you.” And thus Abraham, having patiently waited, obtained the promise. For people swear by something greater than themselves, and in all their disputes an oath is final for confirmation. So when God desired to show more convincingly to the heirs of the promise the unchangeable character of his purpose, he guaranteed it with an oath…”
– Hebrews 6:13-17
“Woe to you, blind guides, who say, ‘If anyone swears by the temple, it is nothing, but if anyone swears by the gold of the temple, he is bound by his oath.’ You blind fools! For which is greater, the gold or the temple that has made the gold sacred? And you say, ‘If anyone swears by the altar, it is nothing, but if anyone swears by the gift that is on the altar, he is bound by his oath.’ You blind men! For which is greater, the gift or the altar that makes the gift sacred? So whoever swears by the altar swears by it and by everything on it. And whoever swears by the temple swears by it and by him who dwells in it. And whoever swears by heaven swears by the throne of God and by him who sits upon it.”
– Matthew 23:16-22
“If a man vows a vow to the Lord, or swears an oath to bind himself by a pledge, he shall not break his word. He shall do according to all that proceeds out of his mouth.”
– Numbers 30:2
“You shall not swear by my name falsely, and so profane the name of your God: I am the Lord.”
– Leviticus 19:12
“Scripture indicates that oaths are generally spoken of negatively, oaths are not inherently wrong (so saying “I swear to God..” isn’t what’s wrong, it’s what you’re tying the oath to), and that Paul himself makes several oaths as does the Lord (and the Lord cannot do evil), so ultimately taking oaths is not forbidden but rather taking false oaths, or committing perjury (1 Timothy 1:10), is forbidden. Jesus and James’ statements are intended to exhort us to speak so truly in our daily lives that we would not even need to use an oath in order to validate our claims. This is obviously unavoidable in legal cases, i.e. when the court requires you to swear under oath, and other random situations, e.g. making a commitment to a stranger (for whatever hypothetical reason) you’ve never met who has no established trustworthiness in you. So we should not swear oaths for the sake of it, but they are not inherently wrong to make when under necessity (e.g. court).”
“In general, the taking of oaths is talked about negatively by Jesus and James. However, God swore oaths, God’s people swore oaths, and Moses’ Law legislated oaths. That would seem to indicate that there is more to the issue than a simple blanket prohibition.”
– Darrell Hamilton, Can a Christian Swear an Oath on a Bible?
“An oath is not intrinsically evil. God bound Himself under an oath to Abraham when He promised to bless the patriarch (cf. Hebrews 6:13-14). With reference to the priesthood of Christ, God “hath sworn… ‘You are a priest for ever after the order of Melchizedek’” (Psalm 110:4). Since the Lord is perfect, one must conclude that an oath per se is not sinful.”
“The Sermon on the Mount has been sometimes called “the ethics of the kingdom”. The point being, that in heaven there will be no need for oaths. What Jesus emphasised is that honest people do not need to resort to oaths, not that they should refuse to take an oath if required by some external authority to do so. Put another way, our daily conversation is to be as sacred as oaths. In ancient history, promises were often introduced by a tremendous formula such as ‘I swear by the archangel Gabriel and all the host of heaven…’ In much the same way, modern honesty is often threatened by forms of exaggeration. In doing so, we devalue our language. The whole point is that Christians should say what they mean and mean what they say. So is it right for a Christian to swear an oath on the Bible? We think yes, there is no prohibition, but add that a Christian lifestyle should be such that truth and integrity means that in ordinary circumstances people will always take you at your word.”
– Defence Anglicans, Is It Right For Christians to Swear an Oath on the Bible?
“There are different kinds of vows and oaths in Scripture, but many passages suggest they’re all dangerous. In the most troubling example, Jephthah, in exchange for a military victory, swore to sacrifice the first thing that walked out his door, and it turned out to be his daughter (Judges 11). Both he and his only child knew there was no alternative. “If a man vows a vow to the Lord, or swears an oath to bind himself by a pledge,” God had commanded, “he shall not break his word” (Numbers 30:2).
The scribes and Pharisees in Jesus’ day adopted rules in an apparent effort to protect the faithful from rash promises: Oaths “by the temple” weren’t binding, for example, but more specific oaths “by the gold of the temple” were (Matthew 23:16ff). Jesus condemned such game-playing and issued a far more expansive rule: “Do not take an oath at all… Let what you say be simply yes or no” (Matthew 5:33-37). In this, he echoed the Law of Moses: “If you refrain from vowing, you will not be guilty of sin” (Deuteronomy 23:22).
Irenaeus, Tertullian, and other early church leaders considered Jesus’ command to be a ban on all oaths, while others like Augustine concluded that Jesus was using hyperbole to condemn abuses. After all, Augustine noted, even Paul took oaths (e.g., Galatians 1:20). Luther, Calvin, and other Reformers sided with Augustine, approving of civil oaths that didn’t abuse or profane the name of God.”
– Ted Olsen, Why Isn’t ‘Yes’ Enough?
“That our Lord does not here forbid the “swearing in judgment and truth,” when we are required so to do by a Magistrate, may appear, (1.) From the occasion of this part of his discourse, — the abuse he was here reproving, — which was false swearing and common swearing; the swearing before a Magistrate being quite out of the question. — (2.) From the very words wherein he forms the general conclusion: “Let your communication,” or discourse, “be, Yea, yea; Nay, nay.” — (3.) From his own example; for he answered himself upon oath, when required by a Magistrate. When the High Priest said unto him, “I adjure thee by the living God, that thou tell us whether thou be the Christ, the Son of God;” Jesus immediately answered in the affirmative, “Thou hast said;” (that is, the truth;) “nevertheless,” (or rather, moreover,) “I say unto you, Hereafter shall ye see the Son of man sitting on the right hand of power, and coming in the clouds of heaven.” (Matthew 26:63, 64.) — (4.) From the example of God, even the Father, who, “willing the more abundantly to show unto the heirs of promise the immutability of his counsel, confirmed it by an oath.” (Hebrews 6:17) — (5.) From the example of St. Paul, who we think had the Spirit of God, and well understood the mind of his Master. “God is my witness,” saith he, to the Romans, “that without ceasing I make mention of you always in my prayers:” (Romans 1:9:) To the Corinthians, “I call God to record upon my soul, that to spare you I came not as yet unto Corinth:” (2 Corinthians 1:23:) And to the Philippians, “God is my record, how greatly I long after you in the bowels of Jesus Christ.” (Philippians 1:8.) Hence it undeniably appears that, if the Apostle knew the meaning of his Lord’s words, they do not forbid swearing on weighty occasions, even to one another: How much less before a Magistrate! — And, Lastly, from that assertion of the great Apostle, concerning solemn swearing in general: (Which it is impossible he could have mentioned without any touch of blame, if his Lord had totally forbidden it:) “Men verily swear by the greater;” by one greater than themselves; “and an oath for confirmation is to them the end of all strife.” (Hebrews 6:16.)”
– John Wesley, Upon Our Lord’s Sermon on the Mount (Discourse 3)
“34. Swear not at all Many have been led by the phrase, not at all, to adopt the false notion, that every kind of swearing is condemned by Christ. Some good men have been driven to this extreme rigor by observing the unbridled licentiousness of swearing, which prevailed in the world. The Anabaptists, too, have blustered a great deal, on the ground, that Christ appears to give no liberty to swear on any occasion, because he commands, Swear not at all But we need not go beyond the immediate context to obtain the exposition: for he immediately adds, neither by heaven, nor by the earth Who does not see that those kinds of swearing were added by way of exposition, to explain the former clause more fully by specifying a number of cases? The Jews had circuitous or indirect ways of swearing: and when they swore by heaven, or by earth, or by the altar, (Matthew 23:18,) they reckoned it to be next to nothing; and, as one vice springs from another, they defended, under this pretense, any profanation of the name of God that was not openly avowed.
To meet this crime, our Lord declares that they must not swear at all, either in this or that way, either by heaven, or by the earth Hence we conclude, that the particle, at all, relates not to the substance, but to the form, and means, “neither directly nor indirectly.” It would otherwise have been superfluous to enumerate those kinds: and therefore the Anabaptists betray not only a rage for controversy, but gross ignorance, when they obstinately press upon us a single word, and pass over, with closed eyes, the whole scope of the passage. Is it objected, that Christ permits no swearing? I reply: What the expounder of the law says, must be viewed in connection with its design. His statement amounts to this, that there are other ways of “taking the name of God in vain,” besides perjury; and, therefore, that we ought to refrain from allowing ourselves the liberty of unnecessary swearing: for, when there are just reasons to demand it, the law not only permits, but expressly commands us to swear. Christ, therefore, meant nothing more than this, that all oaths are unlawful, which in any way abuse and profane the sacred name of God, for which they ought to have had the effect of producing a deeper reverence.
37. But your speech shall be, Yes, yes; No, no Christ now prescribes, in the second place, a remedy; which is, that men act towards each other sincerely and honestly: for then simplicity of speech will have quite as much weight as an oath has among those who are not sincere. Now, this is certainly the best way of correcting faults, to point out the sources from which they spring. Whence comes the great propensity to swearing, but from the great falsehood, the numerous impositions, the unsteady and light conduct, so that hardly any thing is believed? Fairness and honesty in our words are, therefore, demanded by Christ, that there may be no longer any occasion for an oath.
“Yes, yes; No, no.” This repetition means, that we ought to abide by our words, so that all may be convinced of our honesty. Now, as this is the true and lawful method of proceeding, when men have nothing on their tongue but what is in their heart, Christ declares, that what is beyond these comes from evil I do not approve of the exposition of these words which some have given, that the criminality of swearing ought to be charged on the man who does not give credit to what another says. Christ teaches us, in my opinion, that it originates in the wickedness of men, that they are compelled to swear: for, if honesty prevailed among men, if they were not inconsistent and hypocritical, they would maintain that simplicity which nature dictates. And yet it does not follow, that it is unlawful to swear, when necessity demands it: for many things are proper in themselves, though they have had a wicked origin.”
– John Calvin, Commentary on Matthew, Mark, Luke (Vol. 1)
“51. “Again,” says He, “ye have heard that it hath been said to them of old time, Thou shalt not forswear thyself, but shalt perform unto the Lord thine oath: But I say unto you, Swear not at all; neither by heaven, for it is God’s throne; nor by the earth, for it is His footstool; neither by Jerusalem, for it is the city of the great King. Neither shalt thou swear by thy head, because thou canst not make one hair white or black. But let your communication be Yea, yea; Nay, nay: for whatsoever is more than these cometh of evil.” (Matthew 5:33-37) The righteousness of the Pharisees is not to forswear oneself; and this is confirmed by Him who gives the command not to swear, so far as relates to the righteousness of the kingdom of heaven. For just as he who does not speak at all cannot speak falsely, so he who does not swear at all cannot swear falsely. But yet, since he who takes God to witness swears, this section must be carefully considered, lest the apostle should seem to have acted contrary to the Lord’s precept, who often swore in this way, when he says, “Now the things which I write unto you, behold, before God I lie not;” (Galatians 1:20) and again, “The God and Father of our Lord Jesus Christ, which is blessed for evermore, knoweth that I lie not.” (1 Corinthians 11:31) Of like nature also is that asseveration, “For God is my witness, whom I serve with my spirit in the gospel of His Son, that without ceasing I make mention of you always in my prayers.” (Romans 1:9-10) Unless, perchance, one were to say that it is to be reckoned swearing only when something is spoken of by which one swears; so that he has not used an oath, because he has not said, by God; but has said, “God is witness.” It is ridiculous to think so; yet because of the contentious, or those very slow of apprehension, lest any one should think there is a difference, let him know that the apostle has used an oath in this way also, saying, “By your rejoicing, I die daily.” (1 Corinthians 15:31) And let no one think that this is so expressed as if it were said, Your rejoicing makes me die daily; just as it is said, By his teaching he became learned, i.e. by his teaching it came about that he was perfectly instructed: the Greek copies decide the matter, where we find it written, Νὴ τὴν καύχησιν ὑμετέραν, an expression which is used only by one taking an oath. Thus, then, it is understood that the Lord gave the command not to swear in this sense, lest any one should eagerly seek after an oath as a good thing, and by the constant use of oaths sink down through force of habit into perjury. And therefore let him who understands that swearing is to be reckoned not among things that are good, but among things that are necessary, refrain as far as he can from indulging in it, unless by necessity, when he sees men slow to believe what it is useful for them to believe, except they be assured by an oath. To this, accordingly, reference is made when it is said, “Let your speech be, Yea, yea; Nay, nay;” this is good, and what is to be desired. “For whatsoever is more than these cometh of evil;” i.e., if you are compelled to swear, know that it comes of a necessity arising from the infirmity of those whom you are trying to persuade of something; which infirmity is certainly an evil, from which we daily pray to be delivered, when we say, “Deliver us from evil.” (Matthew 6:13) Hence He has not said, Whatsoever is more than these is evil; for you are not doing what is evil when you make a good use of an oath, which, although not in itself good, is yet necessary in order to persuade another that you are trying to move him for some useful end; but it “cometh of evil” on his part by whose infirmity you are compelled to swear. But no one learns, unless he has had experience, how difficult it is both to get rid of a habit of swearing, and never to do rashly what necessity sometimes compels him to do.
52. But it may be asked why, when it was said, “But I say unto you, Swear not at all,” it was added, “neither by heaven, for it is God’s throne,” etc., up to “neither by thy head.” I suppose it was for this reason, that the Jews did not think they were bound by the oath, if they had sworn by such things: and since they had heard it said, “Thou shalt perform unto the Lord thine oath,” they did not think an oath brought them under obligation to the Lord, if they swore by heaven, or earth, or by Jerusalem, or by their head; and this happened not from the fault of Him who gave the command, but because they did not rightly understand it. Hence the Lord teaches that there is nothing so worthless among the creatures of God, as that any one should think that he may swear falsely by it; since created things, from the highest down to the lowest, beginning with the throne of God and going down to a white or black hair, are ruled by divine providence. “Neither by heaven,” says He, “for it is God’s throne; nor by the earth, for it is His footstool:” i.e., when you swear by heaven or the earth, do not imagine that your oath does not bring you under obligation to the Lord; for you are convicted of swearing by Him who has heaven for His throne, and the earth for His footstool. “Neither by Jerusalem, for it is the city of the great King;” a better expression than if He had said, “My [city];” although, however, we understand Him to have meant this. And, because He is undoubtedly the Lord, the man who swears by Jerusalem is bound by his oath to the Lord. “Neither shall thou swear by thy head.” Now, what could any one suppose to belong more to himself than his own head? But how is it ours, when we have not the power of making one hair white or black? Hence, whoever should wish to swear even by his own head, is bound by his oath to God, who in an ineffable way keeps all things in His power, and is everywhere present. And here also all other things are understood, which could not of course be enumerated; just as that saying of the apostle we have mentioned, “By your rejoicing, I die daily.” And to show that he was bound by this oath to the Lord, he has added, “which I have in Christ Jesus.””
– Augustine of Hippo, Commentary on the Sermon on the Mount (Chapter XVII)
“This text has been spun out with many glosses, and many a queer notion and error has been drawn from it, so that many great doctors have been worried about it, and could not become reconciled to the blunt prohibition here that we are to “Swear not at all,” but “let your communication be Yea, yea, and Nay, nay.” So that some have stretched their conscience so tightly, that one doubts whether one ought to take a solemn oath not to avenge himself when he is set free from prison, or whether we are by an oath to make peace and a treaty with the Turks or unbelievers, etc. Now we cannot deny that Christ himself and St. Paul often took an oath; besides, it is said, in the Scriptures, that those are praised who swear by his name; so that also here we must make a distinction, so that we rightly understand the text.
But we have been told sufficiently, that Christ does not wish here to interfere with the secular authority and ordinance, nor to detract at all from the powers that be; but he is preaching here only for the individual Christians, how they are to conduct themselves in their ordinary life. Therefore we are to regard the swearing as forbidden in exactly the same sense as above the killing and the looking upon or desiring a woman. Killing is right, and yet it is also wrong; to desire a man or a woman is sin, and it is not sin; but in this way, that we rightly distinguish both, namely, that it is said to you and to me: if you kill, you do wrong; if you look at a woman to desire her, you do wrong. But to a judge he says: If you do not punish and kill, you shall yourself be punished; likewise to a married man or woman: If you do not cleave to your spouse, you do wrong. So both are right, that one is to kill and not to kill, to be and not to be with a woman; namely, that you do not be wrathful or kill, or look lovingly upon a woman, unless you are specially authorized by God’s word or command to do so. If you are wrathful, however, when God commands you, or if you have a wife according to the word of God, then each is right; for what God says and commands is a very different thing from when you do it of your own accord.
As you have understood that, so understand this also; that the prohibition here is, “Swear not at all,” just as he has entirely forbidden killing, so that there may be no wrath in the heart; in like manner, that we shall keep so aloof from man and woman as not to be looking at them, or thinking upon them to desire them. And it would be a dangerous sermon if we were to apply it to the exercise of governmental authority or to married life, and were to say to the judge, Thou shalt not become indignant, or give practical proof of wrath; or to a wedded pair, Thou shalt not look upon or love thy wife or husband: but we must turn about here and teach the opposite, saying: Thou judge shalt be angry and punish; and every one shall have and love his spouse. How then does Christ say one must desire no woman, and have no wrath in his heart? Answer, as said above, he is speaking of the woman that God has not given you, and of the wrath that is not demanded of you, that you are not to have. But if it is demanded of you, then it is no longer yours, but it is God’s wrath, and no longer your desire, but that which is given and ordained by God; for you have God’s word for it that you shall love your spouse and not desire any other. Thus also in regard to swearing; we must see to it, if we have God’s word for it or not.
That he here insists so much upon the prohibition, that he does also in opposition to their false teachers, who preached in this way, that taking an oath and swearing, although done needlessly and without the word of God, was not sin; yes, they had made a distinction (as Christ here shows) how one might swear freely, and what oaths should be valid or not; as, that one might readily swear by heaven, or by Jerusalem, or by his head; that those were little oaths, and did not have much validity, if only the name of God were not invoked; they had indeed at last carried it so far that a mere yea or nay was of no account, and they held that it mattered nothing if they did not do anything which they had not sworn to do; just as they had taught in regard to killing, that one should not consider a secret anger and spite as sin; the same also, if one were hostile to his wife, had no desire for her or love for her, but had desire for another and proved this by looking at her and sporting with her, and by other signs.
Against such impure saints he began to preach, and says: If you do not become different and more pious you will not enter the kingdom of heaven. The matter of swearing must not be treated as you are doing, who make it right and valid where and when you choose; but the command is, You are not to swear at all, neither by the temple, nor by Jerusalem, nor by your head, as little as by God himself; but let your dealings with each other be yea and nay, and abide by that. For that is an abuse of the name of God, if one to the yea or nay adds oaths and swearing, as if a mere yea and nay were not valid or binding unless the name of God were added. There is also a further abuse, that people swear so thoughtlessly, as is now so commonly done, when they use the name of God with almost every word. That must all be strictly forbidden; as also cursing that is done in God’s name, if it must not be done.
For cursing is just like swearing, both being good and bad. For we read in Scripture that often holy people have cursed; thus, Noah curses his one son, Ham, and the patriarch Jacob pronounced an evil blessing and a curse upon his three sons, Reuben, Levi and Simeon, also Moses against Korah; yes, Christ himself bitterly curses in the psalter his Judas, and in the Gospel the false teachers; and Paul, Galatians 1:9, curses all teachers who preach otherwise (even if it were an angel from heaven), that they shall be anathema, that is, condemned and cursed by God; as if we should say: Let God oppose them and totally destroy them, and give them no mercy or good fortune. So the time may come when one must curse, or do wrong. Thus, that we should now ask God’s blessing upon pope, bishops and princes and wish them success, whilst they with malicious schemes and wicked plottings are seeking to shed the blood of pious people and to throw Germany into confusion; that Christians should not do, but should and must say in regard to it: Dear Lord, curse, and hurl all their scheming to the bottom of hell. Hence, no one can rightly pray the Lord’s prayer without implying a curse. For, when he prays: Hallowed be thy name, thy kingdom come, thy will be done, etc., he must gather up in a mass everything that is antagonistic, and say: Cursed, execrated, disgraced be all other names, and rent asunder and destroyed be all kingdoms that are opposed to thee, gone to ruin be all hostile schemes, wisdom and purposes, etc.
This, however, is the distinction: Of himself no one is to curse or swear, unless he has God’s word for it, that he must curse or swear. For, as above said, where it is done in accordance with the word of God, then it is all right to swear, to be angry, to desire one’s wife, etc. But it is in accordance with the word of God, if he orders me to do it by virtue of my office and on his account, or demands it through those who are in office. Thus, that we may understand it by an illustration, if it should happen that thou art imprisoned, and in the hands of the authorities, and they would demand of thee an oath not to seek for vengeance against them; or, if a prince demands an oath of allegiance; or a judge demands an oath from a witness; then it is your duty to take the oath. For there stands the word, that thou shalt obey the powers that be. For God has so ordained and established government, that one must be under obligations to another, so that all questionable matters may be adjusted, decided and settled by the use of the oath, as the epistle to the Hebrews teaches.
But do you say: Yes, but here stands a different word, that Christ says: Thou shalt not swear. Answer, as above said concerning killing and being angry: Thou, thou shalt not do it, as for thyself. Here, however, it is not thou that swearest, but the judge who orders thee to do it, and it amounts to the same thing as if he did it himself, and thou art now the mouth of the judge. Now Christ here neither commands nor forbids anything to the government, but lets it take its own course as it is bound to do; but he forbids you to swear of your own account, arbitrarily or from habit; just as he forbids to draw the sword, yet does not thereby prevent your being obedient to the government, if your prince had need of your services, or would summon you to go to war; for then you are bound to enter heartily into the work of the war, and it is no longer your hand or sword, but that of the government; and you are not doing it yourself, but your prince, to whom God has committed it. Thus we speak also in similar cases. As, if it should come to pass, that we would make a treaty and concord with our enemies or the Turks, then the emperor and princes could both give and take an oath, although the Turk swears by the devil or his Mahomet, whom he regards and worships as his God, but we worship our Lord Christ and swear by him.
Thus you have now a cause, for which it is right to swear, namely, the necessity of taking an oath from obedience to the government, to confirm the truth or to endure things for the sake of peace and harmony. The other reason is love, though it be not demanded by the powers that be, but is done out of kindness to a neighbor, etc., just as also love is wrathful and rebukes, when it sees a neighbor sin or go astray; as Christ teaches in Matthew 18:15. For it cannot laugh at this or praise what is evil. Thus I may very well show love to the wife of another man, if she be in need or distress, that I may help her out of it; that is not a carnal, forbidden love, but one that is Christian, brotherly, that springs not from my own lust or indiscretion, but because of my neighbor’s need; and it has the sanction of God’s word, which says: “Thou shalt love thy neighbor as thyself.”
Accordingly, if I see any one in spiritual need and danger, weak in faith, or conscientiously fearful, or seriously doubting, and so forth, then I am not alone to comfort, but to asseverate besides, to strengthen his conscience by saying: As sure as God lives and Christ died, so surely this is the truth and the word of God. There an oath is so needful that we cannot do without it. For by that the true doctrine is established, the erring and timid conscience is instructed and comforted, and delivered from the devil. Therefore in such a case you may swear just as hard as you can. Thus Christ and Paul swore, and called God to witness. Thus an oath is suited to every threatening or promise that a Christian preacher preaches, both in alarming hardened sinners and comforting the timid.
In the same way, if one is to vindicate his neighbor or rescue his honor in opposition to bad, malicious tongues, one may also say: Before the dear God you are wrongly accusing him, etc. For this is to use God’s name aright, to the honor of God and the truth, and for our neighbor’s benefit and salvation. For in such a case you have the word and command hovering over you, that orders you to love your neighbor, to rebuke the disorderly, to comfort the sad, etc.; and because it is commanded it cannot be wrong, yes, it even urges you to swear, and you do wrong if you neglect to do it. In short, if you have the word of God [on your side], then may God give you grace right away to swear, to rebuke, to be angry, and to do all that you can. But whatever is aside from this, not commanded, nor for your neighbor’s need or advantage, in that case you should do none of these things. For God wants nothing at all that you do of your own ,notion, without his sanction, be it what it may, even if one could raise the dead. Much less will he tolerate it, that one should abuse his name, appealing to it when there is no need or occasion for it, or that one daily at home and every where else use it improperly, as is now done, when men swear with all they say, especially in beer-houses, so that it were well if this were strictly forbidden and punished. Thus you have a proper, clear understanding of this matter, so that one need not vex himself in vain in regard to this text and make a purgatory out of it when there is none.
Now Christ says: I say to you, Swear not at all, neither by heaven, nor by the earth, nor by Jerusalem. Here we see, the city was held in high esteem and honor, so that they swore by it; and he confirms this, and calls it a city of God, and it is elsewhere also called the holy city. It was holy, however, for this reason, that God’s word was there, and through that God himself dwelt there; and it was a good custom, and no doubt inaugurated by good people, that the city was so highly esteemed, (as the prophet Isaiah also gloriously praises it), not for its own sake, but on account of the word. Accordingly we may well call every city holy that has the word of God, and boast that God is really there.
But that he says: Thou shalt not swear by thy head, for thou canst not make one hair white or black, that he says concerning his creature, not concerning the use we make of it: For he does not mean to say that we cannot powder our hair that it may become black or some other color; but that it is not in our power to bring out a hair that is white or black, nor can we prevent it from becoming thus or otherwise. But when it has grown, then we can cut it off altogether or burn it; just as we can to some extent change one created thing by means of another, but we cannot take any part in having it created so or otherwise. Thus he makes our own head a sanctuary, as that which is not of our work or power, but the gift and creature of God.
That he now concludes: “Let your speech be Yea, yea; Nay, nay,” etc., that he plainly addresses to such as have no command or occasion to swear. For (as was said) of his own accord no one should swear at all. But when these two features are added, command or necessity, then you are not asked to swear for yourself; for you do it not of your own accord, but on his account who demands it of you, namely, your governmental authority, or the need of your neighbor, or God’s command.”
– Martin Luther, Commentary on the Sermon on the Mount