John Gill Commentary Deuteronomy 8:20

"As the nations that Jehovah maketh to perish before you, so shall ye perish; because ye would not hearken unto the voice of Jehovah your God." — Deuteronomy 8:20 (ASV)

As the nations which the Lord destroys before your face, so
shall you perish
Be cut off by the sword, or cast out as they were, the same sins, particularly idolatry, being committed by them. This is to be understood of the seven nations of the land of Canaan, which the Lord would be gradually destroying when Israel came into the possession of their land; and they might righteously expect the same treatment, should they be guilty of the same sins:

because you would not be obedient to the voice of the Lord your God ;
expressed in his law, especially in the two first precepts of it, which require the worship of one God, and forbid the worshipping of idols; or to the Word of the Lord, as the Targum of Jonathan, Christ, the essential Word, in whom the name of the Lord was, and whose voice Israel was to obey, (Exodus 23:20–22) .