Proverbs 20:25 (ESV)

25 It is a snare to say rashly, “It is holy,” and to reflect only after making vows.

In both the Old and the New Testament, one could promise to dedicate (give) something to the Lord if he would answer a certain prayer. This was done, for example, by Hannah (1 Samuel 1:11), David (Psalm 116:14) and Paul (Acts 18:18). It is not wrong to make such a vow to God. But we must do it only after careful consideration. Because God forbids us from breaking our vows (Deuteronomy 23:21–23). A vow that was made in haste can become a “trap.” Think, for example, of a man who promises to give God a big sum of money, but who later cannot afford to give this sum without bringing his family into trouble.

Therefore, let us keep the advice of this proverb in mind, together with the advice in Ecclesiastes 5:2–5: “Be not rash with your mouth, nor let your heart be hasty to utter a word before God.... It is better that you should not vow than that you should vow and not pay.”