Rashi on Deuteronomy 20:4/רש"י על דברים כ׳:ד׳

1כי ה׳ אלהיכם וגו׳ FOR THE LORD YOUR GOD [IS HE WHO GOETH WITH YOU] — They come to war relying on the conquering strength of human beings (lit., flesh and blood) but you come relying on the strength of the Omnipresent God! The Philistines once came to war relying on the strength of Goliath — what was his end? He fell and they fell with him (Sotah 42a).

2ההלך עמכם [FOR THE LORD THY GOD] GOETH WITH THEE — this refers to the camp of the Holy Ark (the camp that has the Holy Ark in its midst, i.e. the camp of the Levites) (Sotah 42a).