Augustine of Hippo, On the Gift of Perseverance Chapter 52: Previous Writings Anticipatively Refuted the Pelagian Heresy

But in respect of their saying “that it was not necessary that the hearts of so many people of little intelligence should be disquieted by the uncertainty of this kind of disputation, since the catholic faith has been defended for so many years, with no less advantage, without this definition of predestination, as well against others as especially against the Pelagians, in so many books that have gone before, as well of catholics and others as our own;” —I much wonder that they should say this, and not observe—to say nothing of other writings in this place—that those very treatises of mine were both composed and published before the Pelagians had begun to appear; and that they do not see in how many passages of those treatises I was unawares cutting down a future Pelagian heresy, by preaching the grace by which God delivers us from evil errors and from our habits, without any preceding merits of ours,—doing this according to His gratuitous mercy. And this I began more fully to apprehend in that disputation which I wrote to Simplicianus, the bishop of the Church of Milan, of blessed memory, in the beginning of my episcopate, when, moreover, I both perceived and asserted that the beginning of faith is God’s gift.