The demons' late, coerced testimony only confirms the prophets
Augustine is answering the claim that pagan books also contained foreknowledge of the overthrow of the gods, and he is now arguing that even such rare, secret demonic predictions do not harm the Christian case.
But what the remaining worshipers of them say—that these things were foreknown and are contained in certain books of their own—although these must be thought fabricated from fulfilled events, even though, if they were true, they ought to have become known to their peoples in their temples so long before, just as our Scriptures are recited as most ancient and most widely known not only in our churches but also—which carries weightier testimony against all enemies—in the synagogues of the Jews. Nevertheless, even those things which are hardly ever and secretly brought forward by them ought not to move us, if it was extorted from some demon to reveal to his worshipers what he had learned from the utterances of the prophets or from the oracles of angels. Why should that not happen, since this is not an attack but an attestation of the truth? For the one thing that alone should be demanded from them—and they have never brought it forward before, nor will they ever attempt to bring it forward afterward except perhaps as something invented—is that their gods dared to predict or say anything through their own seers against the God of Israel. About this God, their most learned authors, who were able to read and know all those things, sought rather to learn who this God was than were able to deny God. Moreover, this God—whom none of them dared to deny is the true God, and even if anyone did deny it, he would not only be subject to due punishments but would also be convicted by certain effects—this God, then, whom no one of them, as I said, dared to deny is the true God, predicted through his own seers, that is, the prophets, with open denunciation that those gods are false and must be utterly abandoned and their temples and idols overthrown; he commanded it with open power; he fulfilled it with open truth. Who, then, would be so foolish as not to choose rather to worship him whom those he used to worship do not forbid him to worship? When he begins to worship him, he will certainly not worship those whom the one he worships forbids him to worship.
Latin
Quod autem dicunt reliqui eorum cultores etiam suorum quibusdam libris haec praecognita contineri, quamquam ex rebus inpletis conficta putanda sint, quae in eorum templis tam longo antea tempore populis eorum, si uera essent, innotescere debuerunt, sicut nostra non solum in ecclesiis nostris, uerum etiam — quod ad grauius testimonium contra omnes inimicos ualet — in iudaeorum synagogis antiquissima et notissima recitantur: tamen nec ipsa ista, quae ab eis uix raro et clanculo proferuntur, mouere nos debent, si cuiquam daemonum extortum est id prodere cultoribus suis, quod didicerat ex eloquiis prophetarum uel ex oraculis angelorum, quod cur non fieret, cum et ista non sit oppugnatio, sed adtestatio ueritatis? illud enim, quod solum ab eis flagitandum est, nec umquam antea protulerunt nec umquam postea nisi forte confictum proferre conabuntur, aliquid deos suos per uates suos contra deum Israhel ausos fuisse praedicere aut dicere. de quo deo doctissimi eorum auctores, qui omnia illa legere ac nosse potuerunt, magis quaesierunt, quis deus esset quam deum negare potuerunt. porro autem deus iste, quem nullus eorum negare ausus est uerum deum, qui et si negaret, non solum subiaceret debitis poenis, uerum etiam certis conuinceretur effectis: iste ergo deus, quem nemo, ut dixi, illorum negare ausus est uerum deum, illos falsos esse deos et omnino deserendos eorumque templa et simulacra euertenda per suos uates, hoc est prophetas, aperta denuntiatione praedixit, aperta potestate praecepit, aperta ueritate conpleuit. unde quis usque adeo desipiat, qui non eum potius colendum eligat, quem coli non prohibent, quos colebat? quem procul dubio cum colere coeperit, illos utique non est culturas, quos prohibet coli quem colit.