John Calvin Commentary Romans 9:18

"So then he hath mercy on whom he will, and whom he will be hardeneth." — Romans 9:18 (ASV)

To whom he wills then he showeth mercy, etc. Here follows the conclusion of both parts, which can by no means be understood as being the language of anyone other than the Apostle; for he immediately addresses an opponent and presents what might have been objected by an opposing party.

Therefore, there is no doubt that Paul, as we have already reminded you, speaks these things in his own person: namely, that God, according to His own will, favors with mercy those whom He pleases, and unsheathes the severity of His judgment against whomever it seems good to Him.

So that our minds may be satisfied with the difference that exists between the elect and the reprobate, and may not seek any cause higher than the divine will, his purpose was to convince us of this: that it seems good to God to illuminate some so that they may be saved, and to blind others so that they may perish. For we should particularly notice these words, to whom he wills, and, whom he wills; beyond this He does not allow us to proceed.

But the word hardens, when applied to God in Scripture, means not only permission (as some superficial interpreters would have it) but also the operation of the wrath of God. For all those external things that lead to the blinding of the reprobate are the instruments of His wrath; and Satan himself, who works inwardly with great power, is to such an extent His minister that he acts only by His command.

Then that frivolous evasion, to which the schoolmen resort regarding foreknowledge, falls to the ground. For Paul teaches us that the ruin of the wicked is not only foreseen by the Lord but also ordained by His counsel and His will; and Solomon teaches the same thing: that not only is the destruction of the wicked foreknown, but the wicked themselves have been created for this very purpose—that they may perish (Proverbs 16:4).