The controversy with Pelagius (d ca. 420) was also important in the development of Augustine's teachings. Pelagius was a monk from Britain known for his zeal and strict discipline He believed that humans had the free will to keep from sinning The fall of Adam (his sin against God in the Garden of Eden) set a bad example but did not doom the race to continue sinning At any given moment people still had the power to choose sin or not. In part, God's grace consisted of sending Jesus to give humans a new example to follow. There were no sinful people, just sinful acts.
Augustine felt that Pelagius failed to understand the power of evil and the destructive nature of sin The fall of Adam had distorted the whole human race and all of the universe. Something deep within people and their world had changed. Even when people were exercising their free will, they did not have the choice of doing something that was entirely good. Every act, every decision was a mixture of good and evil. People were genuinely sinful. It was not just that they commit sinful acts
Because he was convinced that people were so bound to sin, Augustine was driven to accept predestination (some are chosen by God to be saved, others are not), irresistible grace, and the absolute control of God over all that happens. To him, salvation depended entirely on the grace of God breaking into the human to change the heart of that person. Augustine's position was debated for about a century. Eventually Pelagianism was rejected. The church officially accepted salvation by grace alone, but rejected Augustine's more radical ideas on predestination and irresistible grace But the issues of free will, grace, and predestination would continue to be sources of conflict