Pelagianism is a 5th-century Christian "heresy" taught by Pelagius and his followers. It stresses the essential goodness of human nature and the freedom of the human will. Pelagius was concerned about low moral standards among Christians, and he wished to improve their behavior by his teachings. Pelagius rejected the arguments of those who claimed that they sinned because of human weakness; this was simply an excuse for immorality, according to Pelagius. He insisted that God made human beings free to choose between good and evil and that sin is a voluntary act committed by a person against God's law. Celestius, a disciple of Pelagius, denied both original sin and the necessity of infant baptism. Pelagianism was opposed not only by Augustine, but also by Calvin. Most Puritans were Calvinist in their leanings.