Augustine argues against Pelagius that human nature and free will cannot attain righteousness without Christ. Nature was created good, but original sin has wounded the will, leaving humanity dependent on Christ as Physician and Vivifier. Grace is an unmerited necessity for infants and adults alike: it forgives past sins, heals the will, prevents future sin, and justifies. Augustine therefore rejects the claim that those who die without baptism escape original condemnation.

The controversy turns on whether the natural capacity to avoid sin is sufficient for actually doing so. Augustine interprets biblical commands, Paul’s struggle between flesh and Spirit, James’s teaching on the tongue, and the Lord’s Prayer as testimony that divine assistance is indispensable. The flesh signifies sinful desire and works, not the body itself; natural needs such as hunger are not sinful, though weakness can turn them toward sin. Obedience motivated by fear under the law becomes the liberty of love through the Holy Spirit. Perfection is possible only through Christ, prayer, and grace, while earthly believers must continue asking both for help against temptation and forgiveness. Even the righteous require humility, with the Blessed Virgin Mary identified as the unique exception to universal human sin. Augustine closes by presenting catechesis as a formation in faith, good works, warnings, promises, gratitude, and persistent prayer: God’s commands are not impossible because love, poured into the heart by the Spirit, makes them light.