Yahweh said to Gideon, The people are yet too many; bring them down to the water, and I will try them for you there: and it shall be, that of whom I tell you, This shall go with you, the same shall go with you; and of whoever I tell you, This shall not go with you, the same shall not go.
The text does not enable us to understand God’s motive certainly. Simple obedience is what He required. Before God told Gideon to let the larger group of soldiers go home, He gave him a promise that He would deliver Israel with the 300 remaining warriors. This promise undoubtedly encouraged Gideon’s faith.