God expects vows made to Him to be kept. He considers a broken vow to be sin.
GOD told Moses to warn Israel:
22 “If you should make a vow to the Lord your God, you shall not delay to pay it; for the Lord your God will surely require it of you, and it would be sin to you. 23 But if you should abstain from vowing, it is not a sin to you.Deuteronomy 23:22-23 OSB
We have previously established that:
Therefore, GOD always speaks truth. He is Truth, in fact.
Saying you will do something and then not doing it is, at best, failing to keep your word—lack of integrity—and, when intentional, lying.
Lying has always been sin and always will be sin. Therefore, while this passage is given in the context of the Law of Moses, we may safely use the text to apply it to our lives today, because its message is a universal truth for all generations.