It would appear from this verse alone that the congregation is sending the force of 12,000 men in order to launch a second holy war by serving justice on the town for not having sent a contingent to Mizpah. But this is not all the congregation will say on the matter. The next verse reveals the real reason behind their command.
10 So the congregation sent 12,000 of their bravest men there and commanded them, “Go and strike the inhabitants of Jabesh-gilead with the edge of the sword; also the women and the little ones.