Charles Ellicott Commentary Judges 21:3

"And they said, O Jehovah, the God of Israel, why is this come to pass in Israel, that there should be to-day one tribe lacking in Israel?" — Judges 21:3 (ASV)

Why is this come to pass ...? —This is not so much an inquiry into the cause, which was indeed too obvious, but a wail of regret, implying a prayer to be enlightened as to the best means of averting the calamity. The repetition of the name “Israel” three times shows that the nation had not yet lost its sense of corporate unity, even though that unity had often been torn apart by their civil dissensions. Their wild justice is mingled with a still wilder mercy.

One tribe lacking. —The number twelve had an almost mystical significance, and is always preserved in counting the tribes, whether Levi is included or excluded.