Augustine of Hippo — as excerpted in the Catena Aurea on John 12:37-43

“(Tr. liii. 5) But what follows involved a deeper question: Therefore they could not believe, because that Esaias said again, He hath blinded their eyes, and hardened their hearts, that they should not see with their eyes, nor understand with their heart, and be converted, and I should heal them. That they should not believe; but if so, what sin is there in a man doing what he cannot help doing? And what is a graver point still, the cause is assigned to God; since He it is who blinded their eyes, and hardened their heart. This is not said to be the devil’s doing, but God’s. Yet if any ask why they could not believe, I answer, Because they would not. For as it is to the praise of the Divine will that God cannot deny Himself, so is it the fault of the human will that they could not believe.”