What does Judges 1:25 mean?

The tribe of Ephraim wants to capture the city of Bethel. To do so, they seem to be following a plan that worked for capturing and destroying the city of Jericho. They send in spies (Joshua 2:1–7). Those spies contact a man leaving the city. They offer to "deal kindly" with the man, likely by agreeing to let him live, if he will show them a way into the city.

The spies of Jericho made a similar offer to the prostitute Rahab, but she had already expressed faith and loyalty to the God of Israel. This Bethelite has not done so. He shows them a way into the city simply to avoid being killed by the spies of Ephraim. He betrays his own people to save his life and that of his family.

Ephraim's tribe is successful to a point. They conquer Bethel and destroy the city. However, they fail to obey God's command to utterly destroy all the region's inhabitants (Deuteronomy 20:16–18). They let the traitor live and do not even require him and his family to join them. They simply let him go (Judges 1:26).