Is it God or Satan who blinds those who do not believe?

The Bible presents both as true at different levels. Satan is the deceiver who actively blinds; God is the judge who gives over to that blindness those who have refused the light. The clearest sign that these are not rival accounts is that 2 Thessalonians 2 has both in one passage. The lawless one comes “after the working of Satan” with every kind of deceit (2:9–10), and God sends the strong delusion (Greek energeia planēs, ‘a working of error’, 2:11). The same deception is Satan’s work, and it is also God’s judgment, because God lets it take hold of those who have chosen it.

In each of these passages the blinding is set after unbelief, as its judgment. John says that “though he had done so many miracles before them, yet they believed not on him” (John 12:37); only then does he quote Isaiah 6:10. Paul says that the delusion comes “for this cause”: “because they received not the love of the truth” (2 Thessalonians 2:10–11), and “had pleasure in unrighteousness” (2:12). Romans 1 describes the same pattern: because people did not want to keep God in mind, “God gave them over to a reprobate mind” (Romans 1:28). This is a judicial hardening, like Pharaoh’s (see the entry on who hardened Pharaoh’s heart): God confirms people in what they have chosen, and he uses even Satan’s deceit as his sentence.

So Satan blinds as the enemy, people blind themselves by rejecting the truth, and God, as judge, gives them over to it. None of the writers sees these as excluding one another.

How active is God in the hardening?

Christians agree that the hardening is a just judgment, but differ on how to describe God’s part, especially in John 12:39, “Therefore they could not believe”. Calvin and the Reformed tradition see God actively, by a righteous judgment, delivering to blindness those he has not chosen, and using Satan as his instrument. Wesley and the Arminian tradition, and others such as Barnes, stress that God withdraws his restraint and lets people have the error they prefer, so that ‘could not’ describes the settled state their refusal had produced. Both hold that God is never the author of sin and that people remain responsible (see also the entry on whether God wants everyone to be saved).

‘The god of this world’

A few early writers read 2 Corinthians 4:4 as referring to the true God (see the entry on who rules the world). Most take it to mean Satan, as the parallel titles in John 12:31 and Ephesians 2:2 suggest.