For in those people God did not make the common sins but found them there, as we have noted before. And although God, in his just but to us hidden judgment, does abandon and harden them more and more (Romans 9:18), yet it is they who by their own free choice first become hardened (Romans 11:7) and abandon the benefits of general providence; they abuse God’s longsuffering, as Paul testifies in Romans 1:18, 26, and 28.

Thus God is said to harden men, not by positive hardening, or working anything in the creature, but by not working, not softening, leaving a man to the hardness of his own heart, whereby it is unavoidable, by the depravation of man’s nature, and the fury of his passions, but that he should be further hardened. … If you put fire near to wax or resin, both will melt; but when the fire is removed, they return to their natural quality of hardness and brittleness. The positive act of the fire is to melt and soften, and the softness of the rosin is to be ascribed to that, but the hardness is from the resin itself, wherein the fire hath no influence, but only a negative act by a removal of it; so when God hardens a man, he only leaves him to that stony heart which he derived from Adam, and brought with him into the world.

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.

When God is here spoken of as hardening some of the children of men, it is not to be understood that God by any positive efficiency hardens any man's heart. There is no positive act in God, as though he put forth any power to harden the heart. To suppose any such thing would be to make God the immediate author of sin. God is said to harden men in two ways: by withholding the powerful influences of his Spirit, without which their hearts will remain hardened, and grow harder and harder; in this sense he hardens them, as he leaves them to hardness. And again, by ordering those things in his providence which, through the abuse of their corruption, become the occasion of their hardening.

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.