The following is an excerpt from the article Unconditional Reprobation and Active Hardening: A Study on Romans 9:11-22 (this article is a condensed version of a series of sermons preached on the subject):
If all the above Scriptures are not enough to convince the reader that God actively hardens people’s hearts and causes them to sin, the following is one Scripture passage that is so clear that it cannot be refuted by anyone with a sound mind:
“He turned their heart to hate His people, to deal craftily with His servants” (Psalm 105:25).
God turned their heart to hate His people and to deal craftily with His servants. Is it sin, is it wicked, to hate and deal craftily with God’s people? Of course it is. Thus, God turned their heart to sin. What does it mean to turn someone’s heart? In Hebrew, it is an active bending, making, fashioning, forging, causing, and producing. There is no getting around what this verse is saying. God actively made their hearts to think wicked things and then made them do wicked things. And God did not just “leave” them or “permit” them to think and do anything. He made them think and do particular things, particular sins. As seen later in the Psalm, He did this to show forth His power in His wondrous and marvelous works so He would get all the praise and the glory and so His people would worship Him and obey Him.