What does Judges 20:7 mean?

The Levite ends his testimony in front of assembled leaders of Israel (Judges 20:1–3) with a call for their response. He has described the heinous death of his concubine, as well as his gruesome call for justice (Judges 20:4–6). He does not see himself as their leader. Nor does he actively call God's people to war against Gibeah or the tribe of Benjamin.

However, he does deliberately incite moral outrage over Gibeah's sin. He pressures the leadership of the tribes to acknowledge what has happened and to respond in some way. He concludes by asking them to decide what they should do. This was likely a far more effective tactic than if he had demanded they kill everyone involved in this atrocity. The Levite allows them to come to that inevitable conclusion on their own.

Since the tribes have already amassed troops (Judges 20:2), all these details would have already been discussed. Those soldiers would not have been sent in such numbers without the assumption of action (Judges 20:8). The Levite's testimony and the ultimate response from Israel's leaders are more of a formality.