What darkens a person's foolish heart?
Choosing to put God out of one's thinking and choosing to think only in the realm of the human—what is called secular humanism—darkens the foolish heart. This darkening is not God frying the heart; man does it to himself, yet it operates under God's sovereign volition and human free will.
Les explains that when mankind's heart is hardened, it is not that God fries it; man does it to himself, though under the sovereign volition of God. The context describes a person making a wrong choice, living with it, then deciding wrong again and becoming hardened in the process. God may put him on the spot, and Scripture may say God did it, but that is all God did. The same pattern applies to mankind as a whole. When they became vain, their foolish heart was darkened; this became a response of God to their choosing of their will. Everything mankind does under God is based on free will, and though God is sovereign and in total control, the exercise of free will is still ours. As they choose to put God out of their thinking and choose to think only in the realm of the human, what is called secular humanism, their foolish heart was darkened.