What does Judges 4:1 mean?

The downward spiral, a cycle of sin and rescue (Judges 2:16–19), continues. Israel remains faithful to the Lord as long as the judge who delivered them lives. Perhaps the judge keeps alive the needed memories: both the pain of oppression and God's mighty victory on Israel's behalf. Once the judge dies, however, faithfulness to the Lord doesn't remain with the following generations. The allure of the false gods of the land becomes too strong, and the children of the faithful generation fall away into doing "evil in the sight of the Lord."

It should be emphasized that this "evil" went far beyond failing to keep the law of Moses down to the tiniest detail. Any sin would justify God's wrath. In this case, serving Canaanite gods involved everything from participation in gross sexual immorality to the killing of children on fiery altars. The Lord's anger against His people came in response to truly evil practices.