Reprobation

God hardens some men's hearts, as he did Pharaoh's, and he wills to harden them, or he hardens them according to his decreeing will; "Whom he will he hardens", (Romans 9:18) this he does not by any positive act, by infusing hardness and blindness into the hearts of men; which is contrary to his purity and holiness, and would make him the author of sin; but by leaving men to their natural blindness and hardness of heart; for the understanding is naturally darkened; and there is a natural blindness, hardness, and callousness of heart, through the corruption of nature, and which is increased by habits of sinning.

Thus, God is said to harden a wicked man because of his demerits when, being provoked by that man’s impiety, He takes occasion to withdraw granted grace and to do certain things through which He knows that this man will grow worse.

And this is the decree of reprobation, which by no means makes God the Author of sin (the very thought of which is blasphemy), but declares Him to be an awful, irreprehensible, and righteous Judge and Avenger thereof.