What does the Bible say about making vows or oaths?

from the old testament

• Numbers 30:2 is clear about the obligation to carry out any vows we make to the Lord: "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."
• Deuteronomy 23:21 speaks of the sinfulness of not fulfilling a vow in a timely manner: "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" (cf. Ecclesiastes 5:4-5)
• The Mosaic Law put the responsibility of a woman's vow onto the closest man in her life, e.g., her father or her husband; widows and divorced women were responsible for the vows they made (Numbers 30:3-16).
• Jephthah's story exemplifies the foolishness of making rash vows. He vowed to offer up to the Lord whatever came out of his house, and sadly, that was his daughter. It's debatable how he fulfilled that vow (Judges 11:29–40), but the call is the same: do not make rash vows.

from the new testament

• Jesus indicated that being truthful eliminates the need for vows: "But I say to you, Do not take an oath at all . . . Let what you say be simply ‘Yes’ or ‘No’; anything more than this comes from evil" (Matthew 5:34, 37). James later reminds believers of Jesus' words (James 5:12).
• Jesus' point was about honesty, prohibiting vows. In fact, Acts records Paul and other Jewish Christians of the early church continuing to make vows (Acts 18:18, 21:23-24).

implications for today

Witnesses in courtroom dramas "swear to tell the truth, the whole truth, and nothing but the truth." A bride and groom pledge to stay married "for better, for worse, for richer, for poorer, in sickness and in health." Sadly, these vows often are about as weighty as a schoolyard pinky swear in today's world. That's because of the "buts" —"but I wanted to protect my friend, so I had to lie!" "But you don't understand: I fell in love with someone else." The excuses for breaking a vow are often justified by feelings, a poor guide for right and wrong (Jeremiah 17:9). God calls breaking a vow an "abomination" (Proverbs 12:22). If we regularly break our oaths, we're aligning ourselves with the father of lies (John 8:44) rather than the Father of Lights (James 1:17). Whether in a courtroom, in a church aisle, or in a schoolyard, let your "yes" mean "yes" and your "no" mean "no."

But what about vows that were made foolishly, impulsively, or even sinfully? Scripture does not treat every vow as something to be blindly fulfilled at all costs, especially if keeping it would require further sin or contradict God’s commands. While God takes vows seriously, He never calls us to continue in sin in order to “honor” a promise, since obedience to Him always has priority (Acts 5:29). A rash vow like Jephthah’s (Judges 11:29–40) shows the danger of making commitments without wisdom, not a command to follow through on wrongdoing. In situations where a vow would lead to sin, repentance before God is still possible, but it should be approached with humility, not as an excuse for casual disregard of truth. In other words, God calls us to be people of integrity who neither make reckless promises nor use broken ones as a cover for disobedience but who instead pursue truth, wisdom, and obedience above all.