11 The inquirer might bring forward as a difficulty the fact that those in whose books these prophecies are found are not united with us in the gospel. But when convinced that this also is foretold, he would feel how strong the evidence is. The prophecies of the unbelief of the Jews no one can avoid seeing, no one can pretend to be blind to them. No one can doubt that Isaiah spoke of the Jews when he said, "The ox knows his owner, and the ass his master's crib; but Israel has not known, and my people has not considered;" or again, in the words quoted by the apostle, "I have stretched out my hands all the day to a wicked and gainsaying people;" and especially where he says, "God has given them the spirit of remorse, eyes that they should not see, and ears that they should not hear, and should not understand," and many similar passages.
If the inquirer objected that it was not the fault of the Jews if God blinded them so that they did not know Christ, we should try in the simplest manner possible to make him understand that this blindness is the just punishment of other secret sins known to God. We should prove that the apostle recognizes this principle when he says of some persons, "God gave them up to the lusts of their own hearts, and to a reprobate mind, to do things not convenient;" and that the prophets themselves speak of this.
For, to revert to the words of Jeremiah, "He is man, and who shall know Him?" lest it should be an excuse for the Jews that they did not know—for if they had known, as the apostle says, "they would not have crucified the Lord of glory," — the prophet goes on to show that their ignorance was the result of secret criminality; for he says: "I the Lord search the heart and try the reins, to give to every one according to his ways, and according to the fruits of his doings."
Source: Reply to Faustus the Manichaean (New Advent)