And thou shalt consume; literally, eat, devour ( וְאָכַלְתָּ). Unless they consumed them as one consumes food, they would be a snare to them, by tempting them to join in their idolatry.
If thou shalt say in thine heart. The thought might rise in their minds, How can we ever compete with nations so much more powerful than we? But such thoughts they must repress, remembering what God had done for them to Pharaoh and the Egyptians, and resting assured that the same would he do to the Canaanites.