Charles Ellicott Commentary Deuteronomy 9:3

"Know therefore this day, that Jehovah thy God is he who goeth over before thee as a devouring fire; he will destroy them, and he will bring them down before thee: so shalt thou drive them out, and make them to perish quickly, as Jehovah hath spoken unto thee." — Deuteronomy 9:3 (ASV)

Understand therefore. —Literally, the connection seems to be this: The children of Anakim you know—you know also (the same word) today, that it is Jehovah your God Himself who passes over before you, a consuming fire. He will destroy them, and He will make them bow down before you. And you shall make a conquest of them, and speedily annihilate them, according as Jehovah has commanded you.