The fifth argument: By speaking in this way we make God the author of all evil deeds, we make him who is the most just into one who is cruel and savage, and we turn his infinite wisdom into folly. I myself do not deny that such an opinion is commonly expressed by people speaking on the basis of their carnal understanding, so that they form this kind of conception of God when they hear his own statements about his secret judgments. But what sort of justice is it if foolish human reason is allowed to assess the incomprehensible judgments of God, before which Paul trembles in adoration and wonder because he dare not scrutinize them? [Rom. 11:33-34] When Paul himself quotes the blasphemous opinions of the ungodly, he adds that he is speaking “humanly.” [Rom. 3:5] By this word he shows plainly that human beings are bound to judge perversely on such matters, even to the extent of holding ungodly and sacrilegious opinions. Therefore let us turn away from that headlong effrontery of the carnal mind to a pure modesty and reverence for the divine justice. Then we shall understand that God is not made the author of evil deeds when he is said to lead the ungodly where he wills and to accomplish and execute his work through them, but rather we shall acknowledge that he is a wonderfully expert craftsman who can use even bad tools well. We shall be compelled to admire his justice, which not only finds a way through iniquity but also employs that very iniquity to a good end.
The sixth argument: We damn the whole of nature, because we say that everything that man has from his nature is corrupt. Augustine bears witness that it is nothing new for the enemies of grace to hide behind the praise of nature (To Boniface 2; Against Two Letters of the Pelagians 2.1.1, where Augustine is attacking those who use the defense of the goodness of creation against the Manichees as an excuse for undermining the reality of grace). However, lest I should seem thereby to be evading the issue, I reply [ICR 1.15.1; 2.1.1, 10-11] that both Luther and all of us define nature in two ways: first as it was established by God, which we declare to have been pure and perfect, and second as, corrupted through man’s fall, it lost its perfection. We assign the blame for this corruption to man; we do not ascribe it to God. If Pighius rejects this teaching, let him find fault with the apostle who expounds it in nearly identical words. Or if he prefers, we will reply with words from Augustine’s lips, which are contained in his first book to Boniface: “Human beings are the work of God insofar as they are human, but they are under the control of the devil insofar as they are sinner, unless they are rescued from there through Christ.” [Against Two Letters of the Pelagians 1.18.36] So from God they are good, but from themselves they are evil.
…As for his final objection—to which he is prompted by some quite superficial similarities—namely that if your teaching were accepted the whole doctrine of God would be exposed to ridicule, I will say only that a short and quick answer to all of it can be given in a few words. I mean, of course, if we consider separately what is man’s obligation to God and what God does in man. For we ought not to measure by our own ability the duty to which we are bound nor to investigate man’s capabilities with this unaided power of reasoning. Rather we should maintain the following doctrine. First, even if we cannot fulfill or even begin to fulfill the righteousness of the law, yet it is rightly required of us, and we are not excused by our weakness or the failure of our strength. For as the fault is ours, so the blame must be imputed to us. [ICR 2.7.3-5; 3.12.1-2, 4-8] Secondly, the function of the law is different from what people commonly suppose it to be. [ICR 2.7.6-9] For it cannot make [sinners] good but can only convict them of guilt, first by removing the excuse of ignorance and then by disproving their mistaken opinion that they are righteous and their empty claims about their own strength. Thus it comes about that no excuse is left for the ungodly to prevent them from being convicted by their own conscience and, whether they like it or not, becoming aware of their conscience and, whether they like it or not, becoming aware of their guilt. They may not always acknowledge it and admit it but, with the law pronouncing its judgment within, they are aware of it. It also comes about, conversely, that the godly, being thoroughly emptied of all misplaced confidence in themselves, [an attitude] which is true humility indeed, make room for the grace of God, from which they may draw strength. Therefore in issuing commands and exhortations God does not take account of our strength, since he gives that very thing which he demands and gives it for the reason that by ourselves we are helpless.
John Calvin, The Bondage and Liberation of the Will: A Defence of the Orthodox Doctrine of Human Choice against Pighius (pgs. 39-42)