Some people have believed that Jesus here prohibits all oath-taking without exception, regardless of the subject matter and regardless of the occasion. But I think those who have come to this conclusion have not really understood Jesus’ meaning.
We find several passages in the OT in which the Lord speaks of this matter of swearing an oath in his name. He says, for instance, in Deuteronomy,
You shall fear the LORD your God. You shall serve him and hold fast to him, and by his name you shall swear” (Deut. 10:20).There are times when taking an oath in the name of God is not only permitted, but even required, such as in a court of law when an appeal is made to God to witness the proceedings, to ensure justice, and to bring down wrath upon those who might give false testimony. To swear an oath in his name upon such an occasion is actually a way of honoring him. It is an expression of confidence that he governs the affairs of men and will in fact punish perjurers.
The same is also true with respect to vows, promises made either to the Lord or to other people, when someone obligates himself to fulfill certain commitments.
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 (Num. 30:2; cf. Deut. 23:21-23).What Jesus says in the Sermon on the Mount, then, is a summary of these passages: “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.’ ”
What he goes on to say, “But I say to you, Do not take an oath at all”, should not be understood as annulling the OT law. A little earlier Jesus said, “Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them” (Matt. 5:17). Jesus does not set himself up in opposition to the Law of his Father. It is unthinkable that the Father should say, “You shall swear by name,” and that the Son of the Father should say, “You shall not swear at all.” If this were the case, there would be a contradiction in the Godhead.
It should be noted that Jesus permitted himself to be put under an oath when he stood trial. When he was standing before the council, Caiaphas said, “I adjure you by the living God, tell us if you are the Christ, the Son of God” (Matt. 26:63). To adjure means to charge under oath. Up to this point, Jesus remained silent. He didn’t answer a single charge that was brought against him. But he permitted himself to be put under oath, and he answered appropriately.
What Jesus finds fault with is the practice of flippant, needless oaths in everyday conversation. We are told by those who understand something of the times in which Jesus lived that hardly a conversation took place among the Jews where there was not some oath taken. They would swear upon every trivial occasion. This is what Jesus was condemning.
But beyond this, in their legalistic hypocrisy, they determined that there were some forms of swearing—some forms of oath-taking—that obligated a person to perform what he had promised, and others that did not. There was a great deal of convoluted reasoning behind it all, but it seems to have come down to this. If a man made an oath that referred to God, then he was obligated to keep his word; but if he did not refer to God in his oath, then he was not obligated to keep it. One could swear by heaven and earth, by the sun and moon, by the gray hairs of his father, by the grave of his dear departed mother, but if he did not refer to God in his oath, then he was free from obligation. But even here there was a lot of hair-splitting. Swearing became a clever way of lying. One could give credence to his lie by taking ever so solemn an oath, but if he did not swear with just the right formula—with just the right words—he was not bound by it.
Oaths are designed to give assurance of one’s truthfulness, and there are occasions when oath-taking is proper, as in the solemn proceedings of a court of law, the inauguration of a public official who swears to fulfill the duties of his office, in a wedding where the bride and groom pledge themselves to each other for life, etc.
There are formal occasions like these when oath-taking is proper. But the Jews often used oaths and vows simply to aide and abet their deceit. (And we are no different.)
It is in this context that Jesus says, “Make no oath at all.” There should be no need. Our word should be our bond. We should regard a simple yes or no to be as binding as the most solemn oath. This is why Jesus says that in our ordinary day-to-day conversation, we should let a simple yes or no suffice and that whatever goes beyond this proceeds from evil motives.