Charles Ellicott Commentary Deuteronomy 20:1

"When thou goest forth to battle against thine enemies, and seest horses, and chariots, [and] a people more than thou, thou shalt not be afraid of them; for Jehovah thy God is with thee, who brought thee up out of the land of Egypt." — Deuteronomy 20:1 (ASV)

When you go out to battle—that is, generally; not only in the immediate conquest of Canaan. Yet it may be observed that in the writings of Moses it is foreseen that the completion of the conquest will be gradual, and that Israel will have to go to battle many times before all enemies are overcome.

Horses and chariots.—The Israelite army was chiefly, or rather entirely, composed of infantry, in most of the great victories won by them.