What does the Torah say about vows and oaths?

The Torah treats vows (nedarim) as serious, binding speech-acts rather than casual promises. Numbers 30:2 states the general rule: "If a man vows a vow to the LORD, or swears an oath to bind himself by a pledge, he shall not break his word. He shall do according to all that proceeds out of his mouth." The chapter goes on to lay out specific circumstances involving unmarried daughters and wives, where a father or husband has a limited window to nullify a vow he hears; but if he stays silent, the vow stands and becomes fully binding, showing how seriously the text treats the spoken word once it has gone unchallenged. Deuteronomy 23:21-23 sharpens the warning: "If you make a vow to the LORD your God, you shall not delay fulfilling it, for the LORD your God will surely require it of you, and you will be guilty of sin. But if you refrain from vowing, you will not be guilty of sin. You shall be careful to do what has passed your lips, for you have voluntarily vowed to the LORD your God what you have promised with your mouth." The logic here is notable: the Torah does not command anyone to make vows at all — refraining entirely is explicitly sin-free — but once a vow is spoken, delay or default becomes an offense against God directly, not just a broken promise between people. Ecclesiastes 5:4-5 later echoes the same teaching almost verbatim, reinforcing it as settled wisdom rather than an isolated legal technicality. Rabbinic tradition took this seriousness further still, developing the Kol Nidrei prayer recited on Yom Kippur eve specifically to formally annul vows made rashly or under duress over the previous year — a practical response to how binding the Torah considers spoken vows to be.