A working definition of a biblical vow is in order. A vow is “a solemn promise or commitment that is voluntarily made and promptly paid to God.”1 It amounts to a prayer where the person promises God what God would (allegedly) like to receive in exchange for something the person making the vow would like. God did not require anyone to make a vow, though he gives legislation for vows (Leviticus 22:21; Leviticus 27:2; Numbers 6:2; Numbers 15:3, Numbers 15:8).
The Israelites could promise a variety of things in their vows to God. At the same time, God did lay down certain principles for the payment of a vow. First, Numbers 30:2 stipulates that once a man vows a vow to the Lord, he has to keep it (see also Deuteronomy 23:21; Ecclesiastes 5:4–6). Second, in Leviticus 27:1–34 the Lord permits special vows involving animals, houses, or even persons for dedication to him. The animals could be offered to the Lord, but in the case of persons such sacrificing was forbidden, so the Lord legislated monetary substitutes for the person(s) named in the vow. As the Lord was one who kept his word, he expected the same from his people.
So there is nothing inherently problematic about vows.
30 And Jephthah made a vow to the LORD and said, “If you will give the Ammonites into my hand,