'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: 34. But I say unto you, Swear not at all; neither by heaven; for it is God's throne: 35. Nor by the earth; for it is His footstool; neither by Jerusalem; for it is the city of the great King.36. Neither shalt thou swear by thy head, because thou canst not make one hair white or black.37. But let your communication be, Yea, yea; Nay, nay: for whatsoever is more than these cometh of evil.' -- MATT. v.33-37.
In His treatment of the sixth and seventh commandments, Jesus deepened them by bringing the inner man of feeling and desire under their control. In His treatment of the old commandments as to oaths, He expands them by extending the prohibitions from one kind of oath to all kinds. The movement in the former case is downwards and inwards; in the latter it is outwards, the compass sweeping a wider circle. Perjury, a false oath, was all that had been forbidden. He forbids all. We may note that the forms of colloquial swearing, which our Lord specifies, are not to be taken as an exhaustive enumeration of what is forbidden. They are in the nature of a parenthesis, and the sentence runs on continuously without them -- 'Swear not at all ... but let your communication be Yea, yea; Nay, nay.' The reason appended is equally universal, for it suggests the deep thought that 'whatsoever is more than these' that is to say, any form of speech that seeks to strengthen a simple, grave asseveration by such oaths as He has just quoted, 'cometh of evil' inasmuch as it springs from, and reveals, the melancholy fact that his bare word is not felt binding by a man, and is not accepted as conclusive by others. If lies were not so common, oaths would be needless. And oaths increase the evil from which they come, by confirming the notion that there is no sin in a lie unless it is sworn to.
The oaths specified are all colloquial, which were and are continually and offensively mingled with common speech in the East. Nowhere are there such habitual liars, and nowhere are there so many oaths. Every traveller there knows that, and sees how true is Christ's filiation of the custom of swearing from the custom of falsehood. But these poisonous weeds of speech not only tended to degrade plain veracity in the popular mind, but were themselves parents of immoral evasions, for it was the teaching of some Rabbis, at all events, that an oath 'by heaven' or 'by earth' or 'by Jerusalem' or 'by my head' did not bind. That further relaxation of the obligation of truthfulness was grounded on the words quoted in verse 33, for, said the immoral quibblers, 'it is |thine oaths to the Lord| that thou |shalt perform,| and for these others you may do as you like' Therefore our Lord insists that every oath, even these mutilated, colloquial ones which avoid His name, is in essence an appeal to God, and has no sense unless it is. To swear such a truncated oath, then, has the still further condemnation that it is certainly an irreverence, and probably a quibble, and meant to be broken. It must be fully admitted that there is little in common between such pieces of senseless profanity as these oaths, or the modern equivalents which pollute so many lips to-day, and the oath administered in a court of justice, and it may further be allowed weight that Jesus does not specifically prohibit the oath 'by the Lord,' but it is difficult to see how the principles on which He condemns are to be kept from touching even judicial oaths. For they, too, are administered on the ground of the false idea that they add to the obligation of veracity, and give a guarantee of truthfulness which a simple affirmation does not give. Nor can any one, who knows the perfunctory formality and indifference with which such oaths are administered and taken, and what a farce 'kissing the book' has become, doubt that even judicial oaths tend to weaken the popular conception of the sin of a lie and the reliance to be placed upon the simple 'Yea, yea; Nay, nay.'