Matthew 5:33-37 (Luther)

Matthew 5:33. Again you have heard that it was said to the men of old, “You shall not swear falsely, but shall perform to the Lord what you have sworn.”
34. But I say to you: Do not swear at all, either by heaven, for it is the throne of God,
35. Or by the earth, for it is His footstool, or by Jerusalem, for it is the city of the great king.
36. And do not swear by your head, for you cannot make one hair white or black.
37. Let what you say be simply “Yes” or “No”; anything more than this comes from evil.

This text has also been stretched by many glosses, and all sorts of delusions and errors have been drawn from it. It has puzzled many great theologians, who could not understand the blunt prohibition of any swearing whatever, and the command to be satisfied with yes and no. So tautly have some of them stretched their consciences as to doubt whether an oath of nonaggression is legitimate upon release from captivity, or an oath to bind a peace treaty with the Turks or infidels.41 Now, it is undeniable that Christ Himself and St. Paul often swore. Besides, Scripture praises those who swear by His name (Deut. 6:13). Here, too, therefore, a distinction is necessary for the correct understanding of the text.
We have heard often enough that Christ has no intention here of interfering in the order of the secular realm, nor of depriving the government of anything. All He is preaching about is how individual Christians should behave in their everyday life. Therefore swearing should be thought of as forbidden in exactly the same sense as killing or looking at a woman and desiring her was forbidden earlier. Killing is right, yet it is also wrong. Desiring a man or a woman is sinful, and it is not sinful. That is to say, we must make the proper distinction here. To you and to me it is said: “If you kill, you do wrong; if you look at a woman with desire, you do wrong.” But to a judge He says: “If you do not punish and kill, you shall be punished yourself.” And to a husband or wife He says: “If you do not cling to your spouse, you do wrong.” So both regulations stand: “You should kill” and “You should not kill”; “You should have a woman” and “You should not have a woman.” For you must not get angry or kill or look at a woman with desire unless you have a word or command from God to do so. On the other hand, for you to get angry when God commands you to, or for you to have a wife according to the Word of God, is right in both cases; for what God says to you and commands you to do is vastly different from what you do on your own.
You should understand the prohibition of swearing in the same way as you understand those. Here He forbids you to “swear at all.” Earlier He issued such a complete prohibition of killing that even anger in the heart was wrong, and He commanded such an isolation from men and women that it was wrong even to look at them or to think about them with desire. Preaching would be harmful if we used it to interfere with government or with matrimony and said to a judge: “You shall not get angry, and you shall not show or express your anger”; or to a married couple: “You shall not look at each other or be in love with each other.” On the contrary, we must teach the exact opposite here and say: “You, judge, shall get angry and wreak punishment; and everyone shall have and love his spouse.” What does Christ mean, then, when He says that it is wrong to desire a woman and to have anger in the heart? The answer, as we have said above, is this: He means the woman that God has not given you and the anger that is not demanded of you; these you shall not have. But in the event that it is demanded of you, then it is no longer your anger but God’s anger, and no longer your desire but the desire which God has given and ordained; for here you have a word of God that you shall love your own spouse and not desire any other. The same is true in the case of swearing; you must determine whether or not you have a word of God for it.
His rigid emphasis upon the prohibition here was said in opposition to their false teachers, who preached that even taking an unnecessary oath and swearing without a word of God was not sinful. Indeed, as Christ shows here, they had developed a distinction between oaths that were valid and those that were not, thus allowing people to swear freely. For example, if someone were to swear by heaven or by Jerusalem or by his head, those would be little oaths and not very binding—just so long as he did not invoke the name of God. So far had they progressed in this that a mere yes or no meant nothing, and they maintained that it did not matter if they failed to do something which they had not sworn to do. This was just like their teaching on the question of killing. It was not sinful if you nursed a secret anger and spite, or if you hated your wife, had no desire or love for her, but desired another woman and proved this with your glances, your jokes, and in other ways.
He began His sermon against such impure saints and said: “If you do not change and become pious, you will not enter the kingdom of heaven. It will not do to proceed in the matter of swearing as you do, making it right and valid wherever and whenever you please. But this is the command: ‘Do not swear at all, neither by the temple nor by Jerusalem nor by your head, as little as by God Himself.’ But in your dealings with each other, say yes and no, and let it go at yes and no. It is an abuse of the name of God to go beyond this to oaths and swearing, as if a mere yes and no were not valid or binding without the addition of the name of God.” Another abuse is frivolous swearing, as is so common now, attaching the name of God to practically every word. All this must be strictly forbidden, just as there should be no cursing with God’s name.
For cursing, like swearing, can be either good or bad. In Scripture we read that holy people have often cursed. Thus Noah curses his one son Ham (Gen. 9:25). The patriarch Jacob pronounced a malediction and curse upon his three sons, Reuben, Levi, and Simeon (Gen. 49:3–7). Moses did the same against Korah (Num. 16:15 f.). Indeed, in the Psalter, Christ harshly curses His Judas,42 and in the Gospel He curses the false teachers (Matthew 23). And in Galatians 1:9 Paul curses any teacher who preaches otherwise, even if it were an angel from heaven, as ἀνάθεμα, that is, banished and cursed by God; it is as if we were to say: “May God hold them back and destroy them utterly and give them neither grace nor success.” Thus the time may come when it is wrong not to curse. Certainly it would be wrong for us now to bespeak success and the blessing of God upon the venomous schemes and spiteful plans of the pope, the bishops, and the princes, who oppose the Gospel, seek the blood of pious people, and try to pit one German land against another. It is not our Christian duty to do this, but rather to say: “Dear Lord, curse and destroy and throw all their schemes to the abyss of hell.” Therefore no one can pray the Lord’s Prayer correctly without cursing. For when he prays: “Hallowed be Thy name, Thy kingdom come, Thy will be done,” he must put all the opposition to this on one pile and say: “Curses, maledictions, and disgrace upon every other name and every other kingdom! May they be ruined and torn apart, and may all their schemes and wisdom and plans run aground.”
The distinction, however, is in the fact that no one should curse or swear on his own, unless he has a word of God telling him to do so. As we have said, where it is done with the authorization of a word of God, it is all right to swear, to get angry, or to desire a woman. But “the authorization of a word of God” means a command that I do it for His sake in the execution of my office or an order through those who are in office. To give an illustration: If you should happen to be imprisoned by the government and were required to swear an oath of nonaggression, or if a prince demanded an oath of allegiance, or if a judge demanded an oath from a witness—then it would be your duty to take the oath. For there the word stands (Rom. 13:1): “You shall obey the government.” God has so ordained and constituted the earthly realm that one person must bind himself to another, so that all dubious questions may be adjusted, confirmed, and decided by the use of an oath, as the Epistle to the Hebrews says (Heb. 6:16).
But you say: “Yes, but here we read a different word, spoken by Christ: ‘You shall not swear.’ ” The answer is the same as the one we gave earlier with regard to killing and getting angry. You should not do it on your own behalf. But here it is not you that is swearing, but it is the judge who is ordering you to do so. It is tantamount to his doing it himself, and now you are the judge’s mouth. Now, Christ is neither prohibiting nor prescribing anything for the government here, but He is letting this realm take its own course as it should and must. What He is forbidding is unauthorized, capricious, or habitual swearing. Similarly, when He forbids you to draw your sword, He does not mean that you should disobey the government if your territorial prince needs you or summons you to go to war. Then you are obliged to slash away with your sword. For your hand and sword are no longer on their own, but have been subordinated to the government; and you are not doing this yourself, but your prince is doing it, whom God has authorized. We say the same about similar cases. If it should happen that we sign a treaty or pact with our enemies or the Turks, then the emperor and the princes could both give and receive an oath—even though the Turk swears by the devil or Mohammed, whom he regards and worships as his god, the way we worship our Lord Christ and swear by Him.
So here is one cause for which it is right to swear, when it is necessary to take an oath out of obedience to the government, as a confirmation of the truth or as a means of preserving something for the sake of peace and harmony. The other cause is love. Even though an oath may not be required by the government, it may be necessary for the good of our neighbor. In this way love may also get angry and critical when it sees a neighbor sinning or straying, as Christ teaches in Matthew 18:15–17. It cannot treat evil as a laughing matter or as a praiseworthy thing. Similarly, I may show love to another man’s wife, helping her in her need or distress. Such love is not carnal and forbidden love, but Christian and brotherly love. Its source is not my own lust or impertinence, but my neighbor’s need; and it is authorized by a word of God which says (Lev. 19:18): “You shall love your neighbor as yourself.”
Accordingly, if I see someone in spiritual need and danger, weak in his faith or despondent in his conscience or erring in Iris understanding, I must not only console him; but to comfort his conscience, I must also take an oath and say: “This is the truth and the Word of God, just as surely as God lives and Christ died.” Here an oath is necessary, indeed indispensable. For it establishes the true teaching, it instructs and comforts the erring and timid conscience, and it liberates it from the devil. Therefore you may swear here by the highest and holiest thing possible. This is the way Christ and Paul swore, calling God to witness. Thus an oath is in place in every proclamation of threats or of promises that comes from a Christian preacher, whether he is bringing fear to the hardened heart or comfort to the timid.
Similarly, in exonerating a neighbor or rescuing his reputation from the attacks of evil and venomous mouths, it is permissible to say: “By God, you are doing him an injustice.” All this is the proper use of God’s name, for the glory of God, for the cause of truth, and for the good and the salvation of the neighbor. Here you have a word and a command of God hovering over you, commanding you to love your neighbor, to rebuke the disorderly, and to comfort the sorrowful. Because it is a matter of command, it cannot be wrong. Indeed, the very command urges you to swear, and you do wrong if you fail to do so. In short, in the cases where you do have a word of God, may God give you the grace to swear, to rebuke, to get angry, and to do everything you can. But where it would transgress or exceed the Word of God, where it would be neither a matter of divine command nor a matter of your neighbor’s need or benefit, you should not do any of these things. God does not want anything at all on your own initiative without His Word, regardless of what it is, even if you knew how to raise the dead. Much less will He tolerate the abuse of His name by invoking it where it is neither necessary nor beneficial, or by throwing it around at home and everywhere else all the time. Nowadays some people have to add an oath to every word, most of all in the taverns; it would be a good idea if this were strictly forbidden and punished. Thus you have a proper and clear interpretation of this item, and no one has to torture himself unnecessarily over this text and make a purgatory out of it where there is none.
Now, Christ says: “I say to you, Do not swear at all, either by heaven or by the earth or by the city of Jerusalem.” It is evident from this that they greatly respected and honored the city and even swore by it. He substantiates this when He calls it a “city of God,” and elsewhere it is also called “the holy city” (Is. 52:1). But the reason for its being called “holy” was the presence of the Word of God, through which God Himself dwelt there. This great respect for the city was a fine custom, one that was undoubtedly originated by good people; thus the prophet Isaiah praises it gloriously, not on its own account but on account of the Word. In the same way it is proper to call every city “holy” if it has the Word of God, and to make the claim that God is certainly present there.
But the statement: “You shall not swear by your head, for you cannot make one hair white or black,” applies to His creation as such, not to our use of the creation. He does not mean to say that it is wrong to powder our hair and make it black or any other color, but that it is beyond our power to bring out a hair that is white or black or to keep it from changing one way or another. When it has grown out, of course, it can be clipped off or singed. To some extent it is possible to make use of one creature in changing another creature, but it is impossible to make any contribution to its being created in one way rather than in another. Thus He makes even our heads a sanctuary, something that does not belong to our work or power, but is the gift and creation of God.
His conclusion, “Let what you say be simply yes or no,” is obviously addressed to those who have neither authorization nor need for swearing. As we have said, no one should swear on his own authority at all. But the addition of these two elements, either a command or a necessity, means that you are no longer swearing on your own authority. You are not doing it on your own behalf, but on behalf of him who demands it of you—your government or your neighbor’s need or God’s commandment.
Luther, M. (1999, c1956). Vol. 21: Luther's works, vol. 21 : The Sermon on the Mount and the Magnificat (J. J. Pelikan, H. C. Oswald & H. T. Lehmann, Ed.). Luther's Works (21:98). Saint Louis: Concordia Publishing House.