He was a faithful and hard-working shepherd to his people, but he also found time to write extensively. He was an admirer of Jerome, the great translator of Scripture, and Augusting wrote him a letter hoping to establish a friendship. Unfortunately, the letter went astray. Jerome did not receive the letter, and its contents became public knowledge before Jerome even knew it had been written. Because it was a personal letter, Augustine, in addition to saying how much he admired Jerome, had mentioned some criticisms of something Jerome had written. Jerome was furious, thinking Augustine had been publicly speaking against him, and Jerome was willing to make his response into a public argument with the Bishop of Hippo. However, Augustine wrote him another letter, deeply apologizing and explaining what had happened, and Jerome was calmed. Over the ensuing years they had a long, intellectual and friendly correspondence.
St. Augustine was a very productive writer. The works we have (and it is generally assumed that much of his work did not survive) include 113 books and treatises, more than 200 letters, and over 500 sermons. Among the most famous of his writings are his “Confessions,” and “The City of God,” in which he discusses the work of God in history, showing the relationship between the Christian as citizen of an earthly society and the Christian as citizen of Heaven. His third great work is his “De Trinitate” ("On the Trinity"), in which he discusses the doctrine of the Trinity by comparing the mind of man with the mind of God, based upon the fact that man is made in the image of God. He speaks of a Trinitarian structure in the act of knowing something, a Trinitarian structure in the act of self-awareness, and a Trinitarian structure in the act of religious understanding through which man sees himself as made in the image of God.
Perhaps St. Augustine’s most famous attack on heresy was against the Pelagians. There was a man from Britain named Morgan, or in Latin, Pelagius (meaning "islander"), who began to preach about what he saw as a deterioration of moral standards. Pelagius saw Christians living lives which were sometimes immoral, or at least less than exemplary, and who blamed their actions on human frailty. Pelagius gave the reply to this: "No, God has given you free will. You can follow the example of Adam, or the example of Christ. God has given everyone the grace he needs to be good. If you are not good, you simply need to put in more effort." In his argument with Pelagius, St. Augustine asked him about original sin, and he received the reply that there is no such thing. Augustine asked him why, in that case, it was the universal custom to baptize infants, and Pelagius had no answer. St. Augustine saw the teaching of Pelagius as undermining the doctrine that God is the ultimate source of all good, leading the virtuous Christian to feel that he had earned God's approval by his own efforts. The teaching of Pelagius was condemned by the Church because of the clear argumentation put forward by St. Augustine.
At the then-advanced age of seventy-five, St. Augustine, the great and distinguished Bishop of Hippo, died on 28 August 430.
O Lord God, who art the light of the minds that know thee, the life of the souls that love thee, and the strength of the hearts that serve thee: Help us, following the example of thy servant St. Augustine of Hippo, so to know thee that we may truly love thee, and so to love thee that we may fully serve thee, whom to serve is perfect freedom; through Jesus Christ our Lord, who liveth and reigneth with thee and the Holy Spirit, one God, now and for ever. Amen.