Calvin's Institutes of the Christian Religion Chaper 23 of the 3rd book, part of point 5.

Whenever they presume to carp, let us begin to repeat: Who are ye, miserable men, that bring an accusation against God, and bring it because he does not adapt the greatness of his works to your meagre capacity? As if every thing must be perverse that is hidden from the flesh. The immensity of the divine judgments is known to you by clear experience. You know that they are called "a great deep", (Ps. 36: 6.) Now, look at the narrowness of your own minds and say whether it can comprehend the decrees of God. Why then should you, by infatuated inquisitiveness, plunge yourselves into an abyss which reason itself tells you will prove your destruction? When are you not deterred, in some degree at least, by what the Book of Job, as well as the Prophetical books declare concerning the incomprehensible wisdom and dreadful power of God? If your mind is troubled, decline not to embrace the counsel of Augustine, "You a man expect an answer from me: I also am a man. Wherefore, let us both listen to him who says, 'O man, who art thou?' Believing ignorance is better than presumptuous knowledge. Seek merits; you will find nought but punishment. O the height! Peter denies, a thief believes. O the height! Do you ask the reason? I will tremble at the height. Reason you, I will wonder; dispute you, I will believe. I see the height; I cannot sound the depth. Paul found rest, because he found wonder. He calls the judgments of God 'unsearchable;' and have you come to search them? He says that his ways are 'past finding out,' and do you seek to find them out?" (August. de Verb. Apost. Serm. 20.) We shall gain nothing by proceeding farther. For neither will the Lord satisfy the petulance of these men, nor does he need any other defense than that which he used by his Spirit, who spoke by the mouth of Paul. We unlearn the art of speaking well when we cease to speak with God.



From point 11 of the same chapter

Here the words of Augustine most admirably apply: "Since in the first man the whole human race fell under condemnation, those vessels which are made of it unto honor, are not vessels of self-righteousness, but of divine mercy. When other vessels are made unto dishonor, it must be imputed not to injustice, but to judgment," (August. Epist. 106, De Praedest. et Gratia; De Bone Persever., cap. 12.) Since God inflicts due punishment on those whom he reprobates, and bestows unmerited favor on those whom he calls, he is free from every accusation; just as it belongs to the creditor to forgive the debt to one, and exact it of another. The Lord therefore may show favor to whom he will, because he is merciful; not show it to all, because he is a just judge. In giving to some what they do not merit, he shows his free favor; in not giving to all, he declares what all deserve. For when Paul says, "God has concluded them all in unbelief, that he might have mercy upon all," it ought also to be added, that he is debtor to none; for "who has first given to him and it shall be recompensed unto him again?" (Rom. 11: 32, 33.)