“Again you have heard that it was said to your ancestors, ‘Do not take a false oath, but make good to the Lord all that you vow.’ But I say to you, do not swear at all; not by heaven, for it is God’s throne; nor by the earth, for it is his footstool; nor by Jerusalem, for it is the city of the great King. Do not swear by your head, for you cannot make a single hair white or black. Let your ‘Yes’ mean ‘Yes,’ and your ‘No’ mean ‘No.’ Anything more is from the evil one” (Matt. 5:33-37).
An oath is basically calling upon God to be a witness to the truth of a statement. The occasional necessity of an oath for serious matters is accepted by Scripture: “When a man makes a vow to the LORD or binds himself under oath to a pledge, he shall not violate his word, but must fulfill exactly the promise he has uttered” (Num. 30:3), and “When you make a vow to the LORD, your God, you shall not delay in fulfilling it; for the LORD, your God, will surely require it of you and you will be held guilty . . . whatever your tongue utters you must be careful to do, just as you freely vowed to the LORD, your God, with your own mouth” (Deut. 23:22, 24).
The problem was that tradition had permitted all sorts of lesser oaths/vows that were considered morally permissible to break. It became a kind of game by which rather than simply swearing by God that you were telling the truth or would do something, you would instead swear by something else whereby there was an acceptable list of reasons to break the vow/oath. Jesus addresses this in his condemnation of the “blind guides” (Matt. 23:16-22)
Jesus condemned the idea of using levels of oaths to hedge our responsibility to tell the truth or fulfill a promise. Jesus is also warning against speaking and acting in such a manner that the truthfulness of our statements is only believed if sworn by oath. Such a way of living would clearly be contrary to the commandment against lying. This would be similar to the Essenes, who were reported to have taught that “he who cannot be believed without swearing an oath is already condemned.” And yet the Essenes still required an oath to join them and would take an oath in a Jewish court.
In day-to-day life, we should avoid oaths and vows, because they too casually call upon God to be a witness, and such a cavalier attitude toward God is irreverent. If we fulfill the commandments to be truthful and loving, we shall have no need for oaths, for neither our honesty nor motives would be called into question by anyone who knows us. However, there are occasions where the gravity or solemnity of the situation would appropriately call for an oath.