Adam Clarke on Numbers 30:2

If a man vow a vow - A vow is a religious promise made to God. Vows were of several kinds: -

1. Of abstinence or humiliation, see Num 30:13;

2. Of the Nazarite, see Numbers 6;

3. Of giving certain things or sacrifices to the Lord, Lev 7:16;

4. Of alms given to the poor, see Deu 23:21.

The law in this chapter must have been very useful, as it both prevented and annulled rash vows, and provided a proper sanction for the support and performance of those that were rationally and piously made. Besides, this law must have acted as a great preventive of lying and hypocrisy. If a vow was properly made, a man or woman was bound, under penalty of the displeasure of God, to fulfill it.