What does Judges 1:29 mean?

Earlier in the chapter, the writer of Judges reported on a military victory for the "house of Joseph." This most likely meant the tribe of Ephraim (Genesis 48:3–6). They successfully captured the city at Bethel. This great success was tempered by the fact that they allowed one of the residents of Bethel to live in exchange for helping them find a way into the city. That man joined the Hittites and launched a new Canaanite city with the same name as the one destroyed by the people of Ephraim (Judges 1:22–26).

Now Judges calls Ephraim by name in reporting that they also failed to drive out the Canaanites in the city of Gezer, west of Jerusalem and about halfway to the sea. Gezer guarded an important crossroad for all of Palestine. Because they could not or did not remove the Canaanites, the people of the land continued to live among the people of the tribe of Ephraim.

God's purpose for removing the wicked people of Canaan was closely tied to their cancerous, depraved culture (Deuteronomy 7:1–4, 9:4–5). Israel's failure to purge that evil (Deuteronomy 20:16–18) would lead to tremendous suffering, as the rest of the book of Judges will explain.