Pelagius was an Irish monk. On his visit in Rome, he was so much scandalized when he saw people who identified themselves with Christ were still engaging in sin and living immoral lives. Their barbarian lifestyle provoked him. Upon his rebuke, those engaging in such immoral lifestyle responded, saying they could not resist or control their indulging desires. But he believed other way. So, he told them they had to resist themselves from lust and indulgence. God of the Scripture says, “Just do it.”
He believes that human beings have free will and thy are free to make choice of their own. Also, he believes that we are not fully dead (in the spirit) by the effect of sin, and we have to work for our salvation. Basically, he held the view that apart from faith in Christ, salvation is attained through work.
Augustine had a very high respect for Pelagius, as he was the man of his own words. Pelagius lived what he preached, but Augustine countered his wrongheaded doctrine of sin and salvation. He believed that we are fully dead in the spirit. Apart from the work of the Holy Spirit, we cannot help ourselves for salvation. Human beings have sinful nature by virtue of the totally deprived condition. We love to sin, so we sin. It’s not the case that we have to or want to sin. Our free will is tainted with sin in the fall. In this sense, we are free or have free will only to sin than seeking true God.