What does Judges 11:30 mean?

Until recently, Jephthah has been presented as strong, confident, and even wise (Judges 11:7–12). Only recently was it stated God's Spirit was with him (Judges 11:29). Here, however, facing battle with a superior force in the Ammonites, Jephthah's boldness comes across as foolishness. During this part of Israel's history, people often made vows to God, hoping to earn His favor. In that culture, a "vow" was a solemn and unbreakable promise, more binding than how the term "promise" is used in modern English. Vows made to others were serious; those made to the Lord are said to be especially dangerous and dishonorable to break (Numbers 30:1–2).

The writer of Ecclesiastes warned: "When you vow a vow to God, do not delay paying it, for he has no pleasure in fools. Pay what you vow. It is better that you should not vow than that you should vow and not pay. Let not your mouth lead you into sin, and do not say before the messenger that it was a mistake. Why should God be angry at your voice and destroy the work of your hands?" (Ecclesiastes 5:4–7).

Jesus's warning about the nature of vows is concise: "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). In that context, Jesus was warning about using vows and promises to add credibility to one's promises. An honest person keeps their word, without layering on "vows" to prove their sincerity.

Jephthah's vow comes across as especially unnecessary. Commentators are not sure if he's being arrogant, insecure, or even attempting to manipulate the Lord. In any case, he wants God to give him victory over the Ammonites. He vows to make an enormous and tragic sacrifice in exchange for success, rather than trusting God to do what is best for His people.