Faustus complained that arguments from prophecy led only to vicious circles.  ”Believe in Jesus because of the prophets, he imagines a Christian telling a pagan.  ”I don’t believe the Hebrew prophets,” the pagan replies.  ”But Jesus endorses the Hebrew prophets,” the Christian rejoins.  Laughing, the pagan turns away.

Augustine disagreed.  Prophecies were persuasive because one could see the fulfillment.  We might expect Augustine to launch into a detailed analysis of how the prophecies of the Old Testament were fulfilled in the gospel accounts, but he goes elsewhere.  Psalm 2 prophesies that the son of David would rule the kings of the earth, and now “the name of Christ has spread through all the nations far and wide” and “the kings of the earth have themselves now become subject to the rule of Christ for their salvation and that all the nations are serving him,” just as the Psalm “predicted long before.”  Augustine would show the pagan Psalm 72, and, citing passages from Jeremiah, would point to the fact that idols are everywhere overthrown.  If the pagan were troubled by the unbelief of Jews, or the fact that the church is troubled by heresies, Augustine would point to prophecies that predicted precisely that.

In sum:

“this gentile would see from these and other such testimonies of the prophets that what was foretold has now been fulfilled concerning persecution by kings and peoples, the faith of kings and peoples, the abolition of idols, the blindness of the Jews, the proof from the books that they preserved, the madness of heretics, and the excellence of the holy Church, composed of true and genuine Christians,” and therefore he would find nothing more worthy of belief than the prophets.

Augustine is aware that arguments from Old Testament prophecy to the gospel story are vulnerable; the pagan could reply that the gospel writers fudged the life of Jesus to conform it to prophecy.  But the fulfillments that Augustine highlights are within the immediate experience of the pagan interlocutor.  And they all depend on taking Old Testament prophecies about the spread of the gospel quite literally.  It is, we might say, a postmillennial proof from prophecy.