CLAIM: Jesus says, “I say to you, make no oath at all, either by heaven, for it is the throne of God” (Mt. 5:34). Does this mean that we, as Christians, cannot swear to “tell the truth” in a court of law? Are we allowed to make promises or vows during our weddings?
RESPONSE: The problem with oaths is that we are not able to follow through on what we have said. This is making a guarantee that we really can’t fulfill. Two verses later, Jesus says that we are unable to make oaths that we cannot fulfill (“You cannot make one hair white or black”). Jesus’ primary problem with making oaths is the fact that we cannot fulfill them. By contrast, God makes vows, so vows are not intrinsically wrong (Ps. 110:4).
However, vows are appropriate when swearing to tell the truth, because this is within our control. Jesus does say that we can vow to tell the truth. In verse 37, Jesus says, “Let your statement be, ‘Yes, yes’ or ‘No, no’; anything beyond these is of evil” (cf. 2 Cor. 1:17). Paul himself practiced taking oaths of telling the truth. In Galatians 1:20, we read, “I assure you before God that I am not lying.”
Regarding marriage vows, we should be quick to couple our marriage vows with statements about God’s power to help us—not our own. We should be quick to say that we will not be able to keep our vows on our own moral effort. While some would say marriage vows are always inappropriate, we would disagree. Think about it: If we’re not able to make vows regarding our commitment to our spouse in our wedding, then how can we even make the vow of marriage? Surely some vows are appropriate. Jesus’ primary problem with vows is twofold: (1) false vows and (2) vows that we cannot fulfill.
1. False Vows
Regarding false vows, Leviticus states, “You shall not swear falsely by My name, so as to profane the name of your God” (Lev. 19:12). R. Laird Harris writes, “To take the name of God in vain is not merely to use it as a curse word but to invoke the name of God to support an oath that is not going to be kept. A false oath profanes the name of God.”
2. Vows that we cannot fulfill
As totally depraved persons, we shouldn’t make moral vows to change ourselves (“God, I promise that I’ll never do that again!”). Paul speaks against putting “confidence in the flesh” (Phil. 3:3). The Pharisees were those who felt that they could trust in their own moral effort, and these are those who Jesus was attacking. Once we make a vow, we are told to follow through with it:
(Num. 30:2) If a man makes a vow to the Lord, or takes an oath to bind himself with a binding obligation, he shall not violate his word; he shall do according to all that proceeds out of his mouth.
(Eccl. 5:5) It is better that you should not vow than that you should vow and not pay.”
(Deut. 23:21, 23) When you make a vow to the Lord your God, you shall not delay to pay it, for it would be sin in you, and the Lord your God will surely require it of you. 22 However, if you refrain from vowing, it would not be sin in you. 23 You shall be careful to perform what goes out from your lips, just as you have voluntarily vowed to the Lord your God, what you have promised.
For this reason, we shouldn’t rashly make vows that we cannot fulfill.
 Harris, R. Laird. Leviticus. In F. E. Gaebelein (Ed.), The Expositor’s Bible Commentary: Genesis, Exodus, Leviticus, Numbers (Vol. 2). Grand Rapids, MI: Zondervan Publishing House. 1990. 604.