Moses
Deuteronomy 8:12ESV·traditional attribution

lest, when you have eaten and are full and have built good houses and live in them,

John Calvin Reformed @genevareformer

12. Lest when thou hast eaten and art full. He more fully explains what we have already observed, viz., that it might happen, in the gradual course of time, that they should fail in their fear of God and honor for His Law, and therefore should take the greater care lest continual peace and joy should bring this callousness upon them.

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

John Gill Reformed Baptist @doctorgill

And when thy herds and thy flocks multiply,.... Having good pasture for them in so fruitful a land: and thy silver and thy gold is multiplied; by trading with other nations: and all that thou hast is multiplied; children, servants, and substance.