John 12:39

39. Therefore they could not believe. This is somewhat more harsh; because, if the words be taken in their natural meaning, the way was shut up against the Jews, and the power of believing was taken from them, because the prediction of the prophet adjudged them to blindness, before they determined what choice they should make. I reply, there is no absurdity in this, if nothing could happen different from what God had foreseen. But it ought to be observed, that the mere foreknowledge of God is not in itself the cause of events; though, in this passage, we ought to consider not so much the foreknowledge of God as his justice and vengeance. For God declares not what he beholds from heaven that men will do, but what He himself will do; and that is, that he will strike wicked men with giddiness and stupidity, and thus will take vengeance on their obstinate wickedness. In this passage he points out the nearer and inferior cause why God intends that his word, which is in its own nature salutary and quickening, shall be destructive and deadly to the Jews. It is because they deserved it by their obstinate wickedness.

This punishment it was impossible for them to escape, because God had once decreed to give them over to a reprobate mind, and to change the light of his word, so as to make it darkness to them. For this latter prediction differs from the former in this respect, that in the former passage the prophet testifies that none believe but those whom God, of his free grace, enlightens for his own good pleasure, the reason of which does not appear; for since all are equally ruined, God, of his mere good pleasure, distinguishes from others those whom he thinks fit to distinguish. But, in the latter passage, he speaks of the hardness by which God has punished the wickedness of an ungrateful people. They who do not attend to these steps mistake and confound passages of Scripture, which are quite different from each other.