We know that God uses evil for good in the case of the elect, but how does God act toward the reprobate?
In essence, God gives sinners over to their sin and hardens their hearts. This is taught in Romans 1, where we are given a picture of men being given over to more and more sin. This is not the final manifestation of God’s wrath, but it is a form of it (Romans 1:18).
A good illustration of this idea is given to us in Pharaoh. Scripture repeatedly says that Pharaoh hardened his heart, but this hardening is precisely what God promised He would to to Pharaoh beforehand in Exodus 4:21. We should say that Pharaoh hardened his heart, but we also need to affirm that God hardened Pharaoh’s heart. He wanted to harden his heart against God and he wanted to because God decided that he would want to.
Lastly, it should be pointed out that the exact same event or happening might harden some and soften others. When a man has a stroke, this event might cause some of his children to draw close to God for comfort. It may also cause others of his children to harden their hearts and push away from God. In both cases, God is totally sovereign over the man, his stroke, his children, and their hearts.