What does Judges 2:21 mean?

A pattern in the relationship between God and Israel repeats over and over in the book of Judges:

• The people abandon the Lord to worship idols, often in perverse or violent ways.
• The Lord's anger burns at His people Israel for their unfaithfulness to Him; this is "spiritual adultery."
• In His anger, the Lord uses Israel's enemies to bring the people to their knees.
• When Israelite suffering is terrible, God sends a judge—a deliverer—to save the people.
• God maintains His protection so long as that judge lives.
• When the judge dies, the people fall further into sin than before.

Here, the Lord promises not to drive out any of Israel's enemies that were still in the land when Joshua died. The implication is that God would have allowed Israel to take all her allotted territory if they had remained faithful. That was the goal He communicated to them. That was not the path they followed. As a result, they would never come close to possessing all the territory to which they were entitled (Joshua 1:4). Only in the end times will Israel realize full possession of the Promised Land (Revelation 20:1–6).

Those living in unconquered territories will be persistent oppressors and raiders against Israel (Judges 3:1–4). The groups living in conquered territories—those whom Israel failed to destroy (Deuteronomy 20:16–18)—will be a constant source of temptation and spiritual poison (Judges 2:22; 3:5–6).