What does Judges 20:28 mean?

The previous verse revealed that the ark of the covenant of God (Exodus 25:10–22) was at Bethel during the events of this chapter (Judges 20:12–17). It may have been brought to Bethel specifically to be close to the Israelites when they went to battle. The mission of eleven of the twelve tribes is to bring justice for crimes committed in the territory of the tribe of Benjamin. So far, these efforts have not gone well (Judges 20:18–27).

Here, Scripture notes that Phinehas was still serving as priest during this time. Phinehas was the grandson of Aaron, the first high priest over Israel. Phinehas was famous for his intense passion for serving the Lord, especially in deflecting God's anger toward Israel (Numbers 25). The mention of Phinehas here likely means these events happened in the early years in Israel after Joshua's death. That helps explain the unified approach taken by the Israelite tribes, something not as apparent in later stories from this era.

The people of Israel have spent the day fasting and offering sacrifices to the Lord and mourning the loss of approximately one out of eleven soldiers from their massive army. They had brought this same question to the Lord previously, but they are clearly doubting that He is still with them. So, they ask again: Should we attack Gibeah and the Benjaminites, our brothers, a third time? Or should we stop?

In His prior response, the Lord had told them to attack, but had not said they would be victorious. Here, God tells Israel to attack, and that this time they will win. This is the assurance for which the people had hoped.