What does Judges 21:25 mean?

God's intent for His people was that He would provide leadership for them. So long as they followed His law and remained faithful to Him alone, He would provide all they needed. They would live in abundance and have victory over all their enemies without need of a king to control and lead them (Deuteronomy 30:15–20). As the book of Judges notes, this is not what happened.

The writer of Judges ends the book simply, under inspiration from the Lord. He sums up the general theme of every story told in the account so far: these were days when there was no king in Israel. This statement is literal; Israel had not yet formed a central monarchy. It is also symbolic: Israel is spiritually lawless, ignoring their Lord God and doing whatever they'd prefer to do.

Instead of everyone doing what was right in the eyes of the Lord, according to His law, everyone acted according to their own preferences. The result was chaos, evil practices, idol worship, judgment from God, repentance, rescue through a deliverer, and then a repeat of the pattern (Judges 2:16–19). Eventually, the people demanded a king and God lets them suffer the consequences of that choice, as well (1 Samuel 8:19–22).