7 Let us suppose, then, a conversation with a heathen inquirer, in which Faustus described us as making a poor appearance, though his own appearance was much more deplorable. If we say to the heathen, Believe in Christ, for He is God, and, on his asking for evidence, produce the authority of the prophets, if he says that he does not believe the prophets, because they are Hebrew and he is a Gentile, we can prove the truth of the prophets from the actual fulfillment of their prophecies.
He could scarcely be ignorant of the persecutions suffered by the early Christians from the kings of this world; or if he was ignorant, he could be informed from history and the records of imperial laws. But this is what we find foretold long ago by the prophet, saying, "Why do the heathen rage, and the people imagine a vain thing? The kings of the earth set themselves, and the princes take counsel together against the Lord, and against His Christ." The rest of the Psalm shows that this is not said of David.
For what follows might convince the most stubborn unbeliever: "The Lord said unto me, You are my Son; this day have I begotten You. Ask of me, and I will give You the heathen for Your inheritance, and the ends of the earth for Your possession." This never happened to the Jews, whose king, David was, but is now plainly fulfilled in the subjection of all nations to the name of Christ. This and many similar prophecies, which it would take too long to quote, would surely impress the mind of the inquirer.
He would see these very kings of the earth now happily subdued by Christ, and all nations serving Him; and he would hear the words of the Psalm in which this was so long before predicted: "All the kings of the earth shall bow down to Him; all nations shall serve Him." And if he were to read the whole of that Psalm, which is figuratively applied to Solomon, he would find that Christ is the true King of peace, for Solomon means peaceful; and he would find many things in the Psalm applicable to Christ, which have no reference at all to the literal King Solomon.
Then there is that other Psalm where God is spoken of as anointed by God, the very word anointed pointing to Christ, showing that Christ is God, for God is represented as being anointed. In reading what is said in this Psalm of Christ and of the Church, he would find that what is there foretold is fulfilled in the present state of the world. He would see the idols of the nations perishing from off the earth, and he would find that this is predicted by the prophets, as in Jeremiah, "Then shall you say unto them, The gods that have not made the heavens and the earth shall perish from the earth, and from under heaven;" and again, "O Lord, my strength, and my fortress, and my refuge in the day of affliction, the Gentiles shall come unto You from the ends of the earth, and shall say, Surely our fathers have inherited lies, vanity, and things wherein there is no profit.
Shall a man make gods unto himself, and they are no gods? Therefore, behold, I will at that time cause them to know, I will cause them to know mine hand and my might; and they shall know that I am the Lord." Hearing these prophecies, and seeing their actual fulfillment, I need not say that he would be affected; for we know by experience how the hearts of believers are confirmed by seeing ancient predictions now receiving their accomplishment.
Source: Reply to Faustus the Manichaean (New Advent)