Charles Ellicott Commentary Deuteronomy 20:4

"for Jehovah your God is he that goeth with you, to fight for you against your enemies, to save you." — Deuteronomy 20:4 (ASV)

For the Lord your God is he that goeth with you. —“They come in the might of flesh and blood; but you come in the might of the Eternal” (Rashi). So David to Goliath: Thou comest to me with a sword and with a spear, and with a shield; but I come to thee in the name of the Lord of Hosts, the God of the armies of Israel, whom thou hast defied (1 Samuel 17:45). And so the Psalmist: Some trust in chariots, and some in horses: but we will remember the name of the Lord our God (Psalms 20:7).