What does it mean to swear falsely (Matthew 5:33)?

The Lord begins this fourth passage in the series of His examples (vv. 21-26; 27-30; 31-32; 33-37) with the words: "Again, ye have heard that it hath been said by them of old time, Thou shalt not forswear thyself, but shalt perform unto the Lord thine oaths." As in the previous example concerning divorce, this passage does not deal with an express commandment of God, but with one of the traditions of the elders and scribes, most of which arose after the Babylonian captivity. Although these were meant to explain the divine commandments, some, in the course of time, became more important to the Jews than the Word of God itself. Therefore the Lord had to say to them: "For laying aside the commandment of God, ye hold the tradition of men," and, "Full well ye reject the commandment of God, that ye may keep your own tradition" (Mark 7:8-9).

The third commandment, "Thou shalt not take the name of the LORD thy God in vain," and also the ninth commandment, "Thou shalt not bear false witness against thy neighbour," contained the moral basis for the command not to swear falsely, i.e. to commit perjury. But there are other passages in the Old Testament in which the people of Israel are warned of thoughtless swearing. Leviticus 19:12 says: "And ye shall not swear by My name falsely, neither shalt thou profane the name of thy God" (cf. Num. 30:3-4; Deut. 23:22; Zech. 8:17).

On the other hand there were several occasions where, according to the law, an oath had to be taken and in such cases God required of His people that they swear by His name (Deut. 6:13; cf. Ex. 22:11; Lev. 5:1; Num. 5:19-21). The oath then not only served as confirmation of the truth, but was also a solemn vow in the knowledge of the presence of Jehovah, who had once Himself taken an oath before Abraham (Gen. 22:16; Heb. 6:13-20).

All this is summarised in the declaration, "Thou shalt not forswear thyself, but shalt perform unto the Lord thine oaths."

Deuteronomy 23:21-23 plainly warned Israel that once a vow was made it was binding. They were not required to make such oaths, but If they did, no excuse could be allowed for failure to fulfill it. But the Lord Jesus forbids the making of oaths. Swearing an oath involved a vow to do a certain thing in the future. Often God's name Was invoked in these oaths (1Sam.30:15; 1Kings 17:1); but reticence as to using God's name had led to the use of heaven, earth, Jerusalem, and even one's head; and this in turn led to swearing in vain with no intention of keeping a promise.

Christianity has no place for 0aths, whether sworn seriously or in vain. Israel's law had proven man in the flesh to be untrustworthy: they had vowed to keep the law, but had consistently broken it; therefore we must not dare to emphasize the dependability of our word: rather we should depend utterly on the truth of the word of God. This is the effect of grace.

The simplicity of speaking facts - "yea" or "nay" - without the emphasis of oaths of any kind is only normal for those who have been delivered from the bondage of law and saved by pure grace. More than this comes from the evil of man's natural pride.

Concerning the moral condition of the nation, for which it was responsible to God, the curse was on the one hand pronounced over the thief, and on the other hand over him who swore falsely by the name of the Lord. Such a restriction of the motives for the judgment many at first sight seem very strange. But when we give it some thought, we discover in these two words the characteristics of the sin of man. A thief is an evil one who deals unrighteously towards his neighbour; one who swears falsely makes God to be a liar by taking Him as a witness affirming his oath.

It was certainly very wrong of you to take a false oath and still more wrong of those who compelled you to take it for their gain. We do not believe it to be “the unpardonable sin,” but you are bound to confess the sin and get out of a false position. Do not trifle with conscience, else you may get into a state which can only be compared to hell upon earth. No human power should have induced you to tell a lie, much less to swear one!

Though this trespass is directly involved with another person, yet it is "against the Lord," for He is Creator and concerned about how His creatures are treated. One may have lied to his neighbor in reference to something that had been entrusted to him to keep or as to a pledge he had made, or he may have actually cheated his neighbor in some way. Or he may have found what was lost and instead of restoring it to its owner, he had sworn falsely about it. This could not be said to be a sin of ignorance, but he may have resorted to lying because of fear or weakness. Yet he must then not cover the matter over, but confess his sin and fully restore anything that the neighbor had lost and add one-fifth to the value of it.

Though this trespass is directly involved with another person, yet it is “against the Lord,” for He is Creator and concerned about how His creatures are treated. One may have lied to his neighbor in reference to something that had been entrusted to him to keep or as to a pledge he had made, or he may have actually cheated his neighbor in some way. Or he may have found what was lost and instead of restoring it to its owner, he had sworn falsely about it. This could not be said to be a sin of ignorance, but he may have resorted to lying because of fear or weakness. Yet he must then not cover the matter over, but confess his sin and fully restore anything that the neighbor had lost and add one-fifth to the value of it.

The third commandment forbids the taking of God's name in vain. An oath invoking God's name is a most serious matter. Elijah made such an oath to Obadiah, “As the Lord of hosts lives, before whom I stand” (1 Kings 18:15), and that oath was kept. But men would dare to use God's name often when not even intending to keep their word, thus totally in vain, which is gross evil. We know that people today swear by God with no concern about what they are doing. In fact, the Lord Jesus goes further than the law, by telling us “do not swear at all” (Matt. 5:33-37). For man had been proven by the time the Lord Jesus came, to be so untrustworthy that his promises concerning what he would do in the future were of no value. It would be different to swear to the truth of something that has already taken place, when one knows the facts.

The third commandment forbids taking God's name in vain (v.11). This may be done seriously or flippantly. One may seriously swear by God that he will do a certain thing, and then not do it. People are so irresponsible that such things become commonplace to the point of then using God's name flippantly, so that they don't care how offensively they talk. But God is not mocked: He will execute judgment on all who are ungodly, not only for their ungodly deeds, but for "all the harsh things which ungodly sinners have spoken against Him" (Jude 15).

(4) He proceeds now to another matter, in which again what was tolerated under the law is now forbidden in the new morality which He is enforcing. "Thou shalt not forswear thyself, but shalt perform unto the Lord thine oaths," plainly speaks of vowing. There had been great abuse of it, as Israel's history makes manifest: men not hesitating to vow recklessly to God at the dictate of their pride and passion and self-will, to find themselves then entangled by what seemed now their duty. Careless profanity had come in at the heels of this, and God's name been profaned by light appeals to it on every occasion; modified by conscience or the lack of it, by every kind of circumlocution and indirect expression of what they dared not openly give utterance to.

The Lord sweeps into His prohibition all these evasions of the third commandment, putting them into the same category, with that which was once permitted. Man's utter weakness, so fully and simply demonstrated by his inability even to change the color of a hair, is made (at least in part) the basis of the prohibition. God might swear, for He could accomplish, and knew, too, all the consequences of that to which He pledged Himself. Beautifully we find Him doing it when seeking to assure the soul of His creature, so ready to doubt the perfect faithfulness even of his God. "Wherefore God, willing to show unto the heirs of promise the immutability of His counsel, confirmed it by an oath; that by two immutable things" — His word being really as certain as His oath, but not so to man ― "wherein it was impossible for God to lie, we might have strong consolation, who have fled for refuge to lay hold upon the hope set before us" (Heb. 6:13-18).

"Again ye heard that it was said to the ancients, Thou shalt not swear falsely, but shalt render to the Lord thine oaths. But I say to you, Swear not at all; neither by (in) the heaven, for it is God's throne; nor by the earth, for it is his feet's footstool; nor by (toward) Jerusalem, for it is the great King's city. Nor shalt thou swear by thy head, because thou canst not make one hair white or black. But let your word be, Yea, yea; Nay, nay; but what exceedeth these is of evil (or, the evil one)."

Thus the Lord goes far beyond perjury or breaking a vow. He prohibits swearing altogether in the intercourse of daily life. Our word therein is to be, Yea, yea, or Nay, nay. That which is more than these has no sanction from God, and is therefore of evil, or the evil one, the enemy of God and man. All such asseveration as the Lord illustrates from the facts of Jewish habit arose from the constant experience of men in deceiving or evading. They therefore resorted to such means of insuring the truth. But these efforts defeated themselves; for we know from a reliable Jewish contemporary of the N.T. inspired writers that oaths by earth, heaven, sun, stars, and the entire universe, were not counted binding. Only those obliged the conscience which were by God's name direct and express; nay others might be transgressed. As the Lord supposed in those He addresses poverty of spirit and purity of heart, He proscribed absolutely all such swearing as offensive to God and incompatible with the place of His sons.