Saint Augustine bases his beliefs concerning sin on theological considerations. This has to be the situation because sin is an act in thought, word, or deed that goes against God. Ultimately, the sin is offensive to God due to the fact that sin separates the human spirit from the Divine. Because God is Love, sin removes humankind from that Love, a condition most undesirable. Saint Augustine says: "Hear me, God. Alas for man's sin. So says man and you pity him; for you made him, but you did not make sin in him" (Confessions 23). Humankind has made sin, not God. Sin is part of the theology of Christianity, and Saint Augustine's approach is to view theology as a way to deal with sin.
When Saint Augustine discusses sin, he frequently reaches back to his own schooldays, and the problems he had with sin when he was a boy and young man. But in talking about sin, Saint Augustine must extend his research all the way back to Original Sin and the Fall.
Saint Augustine believed that Adam, before the Fall, possessed free will. He could have chosen not to sin. However, as Adam and Eve ate the apple, corruption entered into them and all of their descendants. Thus, all humankind is tainted with Original Sin, and free will cannot remove this stain. Only God's grace can save humanity from the eternal damnation of Adam's sin. But we are free to pursue good or evil as we desire.
If we love God and our fellow humans, we will select a virtuous way of life, with the hope that Divine Grace will eventually save us. Obviously, Saint Augustine founds his concept of sin on theological arguments. As he states: "Of the world therefore are all humankind, created indeed by the true God, but generated from Adam as a vitiated and condemned stock; and then are made into a kingdom no longer of the world, all from thence have been regenerated in Christ" (Political Writings 295).
Regardless of how humankind may be free to perform good acts...