I wrote to your bishop, the saintly Ambrose, to tell him of my past errors and the purpose I now had in mind. I asked him to advise me which books of Scripture it would be best for me to study, so that I might be better prepared and more fitted to receive so great a grace. He told me to read the prophet Isaiah, presumably because the Gospel and the calling of the gentiles are foretold more clearly in that book than in any other.

Saint Augustine, Confessions, Book IX.5.