What does Numbers 31:6 mean?

Moses sent these twelve thousand men out to war, along with Phinehas, the son of Eleazar the priest. Phinehas brought with him some of the sacred objects and the trumpets used to signal in battle. Numbers 31:6 - Modern Text Bible

(Phinehas, a respected priest, goes with the army, carrying religious items and trumpets. This shows that the battle is seen as a spiritual mission, not just a military one.)