Charles Ellicott Commentary Judges 7:4

"And Jehovah said unto Gideon, The people are yet too many; bring them down unto the water, and I will try them for thee there: and it shall be, that of whom I say unto thee, This shall go with thee, the same shall go with thee; and of whomsoever I say unto thee, This shall not go with thee, the same shall not go." — Judges 7:4 (ASV)

The people are yet too many. —A fresh trial of faith; but small numbers were essential for the method of victory by which God intended that the deliverance should be achieved.

Unto the water. —i.e., to the spring of Harod.

I will try them. —The Septuagint renders it (Codex Vaticanus), “I will purge them,” as gold from dross, and this is the literal sense of the word (Isaiah 1:25; Isaiah 48:10).