Voluntary expressions of devotion usually fulfilled after some condition had been met. Vows in the Old Testament usually were conditional. A common formula for vows was the “if… then…” phrase (Genesis 28:20;
Judges 11:30). The one making the religious vow proposed that if God did something (such as give protection or victory), then he or she in return would make some act of devotion. Not all vows, however, were conditional. Some, such as the Nazirite vow (Numbers 6:1), were made out of devotion to God with no request placed upon God. Whether conditional or not, the emphasis in the Bible is on keeping the vow. A vow unfulfilled is worse than a vow never made. While vows do not appear often in the New Testament, Paul made one that involved shaving his head (Acts 18:18).
These dictionary topics are from the Holman Bible Dictionary, published by Broadman & Holman, 1991. All rights reserved. Used by permission of Broadman & Holman.
Butler, Trent C. Editor.. "Entry for 'VOWS'". "Holman Bible Dictionary".