No one since St. Paul has shaped the beliefs of Christians more than Augustine. He was no innovator; in fact he found his theology largely in St. Paul’s Epistles, but he developed and stressed certain themes. His teaching on grace and free will, faith, predestination, the need for confession, discipline and the last judgment, have become the accepted tenets of both Catholic and Protestant churches. The most important of these tenets are perhaps the first two, grace and free will, and we illustrate Augustine’s views on them, not from his formal treatises, but from a letter to Archbishop Hilary of Arles, a semi-Pelagian. Pelagius, as we have seen, was one who ‘boasted of personal ability’ to follow the Christian life; Augustine was far too conscious of his own weakness and need of supernatural grace. The literal meaning of ‘grace’ is free gift.
Source: Augustine, Letters 157