The sin of Gibeah resulted in its total destruction (v.37). And for standing in solidarity with sin, the entire tribe of Benjamin paid a heavy price. Their fighting force was decimated, their towns were leveled, and even their animals were destroyed (v.48) But, not before Israel's commitment was tested.
In this chapter we see that Israel sought the Lord's direction, obeyed His instruction, and then was pummeled by Benjamin. We don't know exactly why God allowed Israel to suffer two massive defeats at the hand of Benjamin. What we do know is that those first two battles weren't the end of the story and that Israel kept seeking God's direction through it all, and on the third day of battle Israel was victorious over Benjamin and Gibeah (vv.29-48).
The Truth: “I will lift up my eyes to the hills— From whence comes my help? My help comes from the Lord, Who made heaven and earth.” (Psalm 121:1-2)