45 Faustus has an evasive objection, which he no doubt thinks a most ingenious way of eluding the force of the clearest evidence of prophecy, but of which one is unwilling to take any notice, because answering it may give it an appearance of importance which it does not really possess. What could be more irrational than to say that it is weak faith which will not believe in Christ without evidence? Do our adversaries, then, believe in testimony about Christ? Faustus wishes us to believe the voice from heaven as distinguished from human testimony.
But did they hear this voice? Has not the knowledge of it come to us through human testimony? The apostle describes the transmission of this knowledge, when he says: "How shall they call on Him on whom they have not believed? And how shall they believe in Him of whom they have not heard? And how shall they hear without a preacher? And how shall they preach except they be sent? As it is written, "How beautiful are the feet of them who publish peace, who bring good tidings!" Clearly, in the preaching of the apostles there was a reference to prophetic testimony.
The apostles quoted the predictions of the prophets, to prove the truth and importance of their doctrines. For although their preaching was accompanied with the power of working miracles, the miracles would have been ascribed to magic, as some even now venture to insinuate, unless the apostles had shown that the authority of the prophets was in their favor. The testimony of prophets who lived so long before could not be ascribed to magical arts. Perhaps the reason why Faustus will not have us believe the Hebrew prophets as witnesses of the true Christ, is because he believes Persian heresies about a false Christ.
Source: Reply to Faustus the Manichaean (New Advent)