In the matter of oaths and vows, there is much to keep in mind. Once we have determined that we are called by God Himself to swear oaths (Deut. 6:13), there are numerous matters that must be addressed. When should we swear oaths? May we lawfully swear an oath that leads to sin? If we were to make such an oath, are we compelled to keep it? Though some questions may seem to have easy answers, these answers have not been self-evident to all.
First, it bears emphasizing that oaths are for extraordinary occasions. Since oaths are to be made in the name of God and since we must regard that name as supremely holy, we must use special care whenever we invoke it in public and even in private. If we use the Lord’s name every time we make a promise, we will be in danger of coming to view the name of our Creator as a common or ordinary thing. We know that God is gracious and does not strike us every time we sin, including those times in which we take His name in vain. Yet we dare not let that reality make us confident that a flippant use of His glorious name will be overlooked. If we are reserved in the use of His name, we will be less likely to treat it inappropriately and thus less apt to break the third commandment (Ex. 20:7). Additionally, if we make oaths for every promise we make, we increase the number of occasions on which we might break an oath and incur divine discipline. So, it is both wise and safe to reserve the use of God’s name and make vows for only the most solemn occasions, such as when we make a marriage covenant or join the covenant community of the Lord’s people.
Second, let us never forget that we are not permitted to make a vow to sin or a vow that leads to sin. God forbids us from sinning; in fact, we are called to be perfect as He is perfect (Matt. 5:48). Of course, this is a standard we cannot meet in our fallen condition, so we trust in Jesus alone for our justification (Rom. 3:21–26; 2 Cor. 5:21). But it remains true that we are not permitted to sin, so we therefore may not make a vow to sin. A vow to sin is an unlawful vow.
Finally, we must note that the only vows we must keep are lawful vows. It is key that we think very carefully before we make a vow, lest we make one that is unlawful. Take Jephthah for example. He rashly made an unlawful vow to sacrifice his daughter and then ended up keeping it when he should not have done so. He is a sad reminder of the danger of making an unlawful vow and the foolishness of keeping an unlawful promise (Judges 11:29–40).