What does Judges 11:27 mean?

Jephthah has made a clear case that the Ammonites have no valid reasons to attack the Israelites in Gilead. He sent messengers from his own military encampment in Mizpah to the king of Ammon, gathered with his own army for war not far away (Judges 11:4).

The king of Ammon claimed Israel took land that rightfully belonged to his people several centuries earlier. He even demanded Jephthah restore it "peaceably," a veiled threat that an invasion was imminent (Judges 11:13). Jephthah's long response offered at least four arguments for why the king of Ammon was wrong in this claim (Judges 11:14–26). Now he concludes his message with a simple statement: I've done nothing wrong to you. You do wrong by making war on me. This summarizes the Ammonite aggression as an unjust power grab for land and power at the expense of the Israelites.

Jephthah's message frames the entire conflict as a personal matter, though he has only become the leader of Gilead days earlier (Judges 11:5–11). His message pictures this war as a wrongful attack by the king of Ammon on his own person. As far as Jephthah is concerned, he is Gilead.

And yet, Jephthah concludes by clearly stating that God, not Jephthah himself, will decide the matter between the Israelites and the Ammonites. In this way, Jephthah expresses his trust in the Lord's power to save Israel. He trusts the Lord's justice in deciding the dispute, even on the battlefield.