Better is it that thou shouldest not vow. There is no harm in not vowing (Deuteronomy 23:22); but a vow once made becomes of the nature of an oath, and its non-performance is a sin and sacrilege, and incurs the punishment of false swearing.
We gather from the Talmud that frivolous excuses for the evasion of vows were very common, and called for stern repression, One sees this in our Lord's references (Matthew 5:33-37; Matthew 23:16-22).
St. Paul severely reprehends those women who break their vow of widowhood, "having condemnation, because they have rejected their first faith" (1 Timothy 5:12).