Moses
Deuteronomy 8:20ESV·traditional attribution

Like the nations that the LORD makes to perish before you, so shall you perish, because you would not obey the voice of the LORD your God.

Matthew Henry Presbyterian @wholebiblehenry

Moses, having mentioned the great plenty they would find in the land of Canaan, finds it necessary to caution them against the abuse of that plenty, which was a sin they would be the more prone to new that they came into the vineyard of the Lord, immediately out of a barren desert. I. He directs them to the duty of a prosperous condition, Deu 8:10.

Commenting on Deuteronomy 8:10-20

Keil & Delitzsch Lutheran @keilanddelitzsch

Deu 8:19-20 To strengthen his admonition, Moses pointed again in conclusion, as he had already done in Deu 6:14 (cf. Deu 4:25.), to the destruction which would come upon Israel through apostasy from its God.

Commenting on Deuteronomy 8:19-20