One of the central themes of the book of Deuteronomy is the call to remember who God is an what He has done. Before the Israelites enter the promised land, God reminded them of a time when they were led astray, how He humbled them and put them in a place where there is no one to depend but God. God did not test the hearts of men to reveal for already what's inside the heart of men. But God tested his people so they may know the condition of their own hearts. When abundance comes, pride can easily set in the hearts of men. When people start to think that it is through their talent and the work of their hands that gave them wealth, then God's hand of warning will remind them otherwise.