What does Judges 2:3 mean?

God is appearing in some physical, visible form. This might be as a generic human being, or even as a pre-incarnate presence of God the Son. These appearances are often described as "the angel of the Lord." He has come to rebuke the people of Israel for failing to keep their covenant with Him (Judges 2:1–2). They have disobeyed by not driving out the Canaanites from the Promised Land. They have not torn down the altars to false gods. They have made covenants with the people, instead.

God had warned Israel from the beginning what the consequences of this would be: "You shall make no covenant with them and their gods. They shall not dwell in your land, lest they make you sin against me; for if you serve their gods, it will surely be a snare to you" (Exodus 23:32–33).

That's why God wanted Israel to completely rout and destroy the Canaanites (Deuteronomy 20:16–17), to keep His people from getting drawn into the worship of their gods: "…that they may not teach you to do according to all their abominable practices that they have done for their gods, and so you sin against the Lord your God" (Deuteronomy 20:18).

Now the Lord declares that He will not work to remove the evil Canaanites. Instead, they will remain and become a source of great misery. Likewise, their false religion will become a disastrous temptation for Israel. The next few centuries will be much more difficult, much more tragic, than if they had obeyed the Lord. These hardships make up much of the content of the rest of the book of Judges.