Why is the foolish heart of those who reject God darkened?
The foolish heart is darkened because people willfully choose to put God out of their thinking and think only in the human, secular realm. Their darkened heart is a response from God to that choice, under His sovereign control. Man hardens himself by repeated wrong decisions, not because God fries his heart.
Les explains that when Scripture speaks of man's heart being hardened, it is not that God fries it. Man does it to himself, yet it is under the sovereign volition of God. The same pattern applies to mankind as a whole. When they became vain and their foolish heart was darkened, it was a response of God to their choosing of their will. Everyone constantly faces choices, and even though God is sovereign, free will is still ours to exercise. Choosing to put God out of their thinking and think only in the human, secular humanism realm results in that darkened foolish heart. Les points back to Psalms 14 for this truth.