"They did not dislodge the Canaanites living in Gezer; to this day the Canaanites live among the people of Ephraim." (Joshua 16:10)
Joseph's descendants receive their allotment: Ephraim in chapter 16, the other half-tribe of Manasseh in chapter 17. Ephraim's territory is described with its boundaries and towns. But the chapter ends with a compromising note: They did not dislodge the Canaanites living in Gezer; to this day the Canaanites live among the people of Ephraim but are required to do forced labour. The incomplete obedience, the Canaanites kept as servants rather than driven out as commanded, is the early symptom of the disease that will corrupt Israel in Judges. They received the benefit of Canaanite labour while violating the divine command.
The Catechism identifies this kind of compromise, the toleration of what God commanded to be removed because it seems useful, as the root of apostasy: the things kept for their convenience will eventually become the things that draw the people toward their gods (CCC 2113). Gezer's Canaanites remained, and the tolerated Canaanites became the teachers of Baal worship to the very tribe that should have driven them out.
Brothers and sisters, the Canaanites kept as servants became the teachers of idolatry. The things you keep for their usefulness while knowing they should be removed always exact the same price eventually. The cost of incomplete obedience is paid later, in the tribe's apostasy rather than the general's inconvenience. Drive out what was commanded to be driven out.
Lord God, give us the courage to complete the task even when incomplete obedience seems convenient. The Canaanites kept for labour became the destroyers of faith. Deliver us from every tolerated compromise. Through Christ our Lord. Amen.