4 And here we meet with the second question, to treat of which, indeed, in any adequate manner, to investigate all its mysterious windings, and throw them open to the light in a befitting way, I think within the scope neither of my own powers, nor of the shortness of the time, nor of your capacity. Yet, as we cannot allow ourselves so far to disappoint your expectations as to pass on to other topics without saying something on this, take what we shall be able to offer you: and wherein we fail to satisfy your expectations, ask the increase of Him who appointed us to plant and to water; for, as the apostle says, “Neither is he that plants anything, nor he that waters; but God that gives the increase.” There are some, then, who mutter among themselves, and sometimes speak out when they can, and even break forth into turbulent debate, saying: What did the Jews do, or what fault was it of theirs, if it was a necessity “that the saying of Isaiah the prophet should be fulfilled, which he spoke, Lord, who has believed our report and to whom has the arm of the Lord been revealed?”
To whom our answer is, that the Lord, in His foreknowledge of the future, foretold by the prophet the unbelief of the Jews; He foretold it, but did not cause it. For God does not compel any one to sin simply because He knows already the future sins of men. For He foreknew sins that were theirs, not His own; sins that were referable to no one else, but to their own selves. Accordingly, if what He foreknew as theirs is not really theirs, then had He no true foreknowledge: but as His foreknowledge is infallible, it is doubtless no one else, but they themselves, whose sinfulness God foreknew, that are the sinners.
The Jews, therefore, committed sin, with no compulsion to do so on His part, to whom sin is an object of displeasure; but He foretold their committing of it, because nothing is concealed from His knowledge. And accordingly, had they wished to do good instead of evil, they would not have been hindered; but in this which they were to do they were foreseen of Him who knows what every man will do, and what He is yet to render unto such an one according to his work.
Source: Tractates on the Gospel of John (New Advent)