original sin, in Christian theology, the sin of Adam Adam (ăd`əm), [Heb.,=man], in the Bible, the first man.
..... Click the link for more information. , by which all humankind fell from divine grace grace, in Christian theology, the free favor of God toward humans, which is necessary for their salvation. A distinction is made between natural grace (e.g., the gift of life) and supernatural grace, by which God makes a person (born sinful because of original sin )
..... Click the link for more information. . Saint Augustine Augustine, Saint (ô`gəstēn, –tĭn; ôgŭs`tĭn), Lat.
..... Click the link for more information. was the fundamental theologian in the formulation of this doctrine, which states that the essentially graceless nature of humanity requires redemption to save it. The purpose of baptism baptism [Gr., =dipping], in most Christian churches a sacrament . It is a rite of purification by water, a ceremony invoking the grace of God to regenerate the person, free him or her from sin, and make that person a part of the church.
..... Click the link for more information. is to wash away original sin and to restore the individual to an innocent state, although even after baptism a tendency to sin remains as a result of original sin.

original sin

In Christian doctrine, the condition or state of sin into which each human being is born, or its origin in Adam's disobedience to God when he ate the fruit of the tree of knowledge of good and evil. His guilt was transmitted to his descendants. Though Genesis describes Adam's sufferings as the consequence of his disobedience, it does not make Adam's sin hereditary. The main scriptural basis of the doctrine is found in the writings of St. Paul; St. Augustine helped make humanity's sinful nature a central element in orthodox Christian theology. Medieval theologians continued to explore the issue, and Thomas Aquinas offered a more optimistic view of human nature in his teachings on original sin than had Augustine. Martin Luther and John Calvin accepted a more Augustinian understanding, and modern evolutionary theory and biblical source criticism raised new challenges for the definition of original sin.