Original Sin is the sin which all the descendants of Adam inherit from their first progenitor. The doctrine of Original Sin is a first postulate of Christianity in the scheme of man's redemption by Christ. The first explicit statement is to be found in by Paul in the book of Romans: "As through one man sin came into the world, and death by sin, and so death penetrated to all men, because all sinned... for if by the trespass of one the many died, much more the grace and the gift in the grace of the one man Jesus Christ abounded to the many."
The ante-Nicene Greek Fathers say little about the doctrine, and this only incidentally. When they do mention the subject it is always in the spirit of Saint Paul's statement, that all mankind fell in Adam, and that through this first sin death entered into the world, the will became weakened, reason obscured, and concupiscence disordered. There is also little to be gathered from the Latin Fathers of the ante-Nicene Age, for the doctrine had not become the subject of controversy, and so awakened but slight theological discussion or formulation. Wherever mentioned by them, the prevailing idea at bottom was the Pauline doctrine of the fall of the human race in Adam, with its dire consequences, which are to be remedied only by the grace and merits of Christ.
Augustine was the first-Latin Father to treat it systematically and extensively in his controversy with the Pelaeians in relation to grace, free-will, predestination, etc. His teaching is succinctly stated in the following passage: "He (Adam), exiled after sin, bound his offspring also, which by sinning he had corrupted, as it were in the root, under the penalty of death and condemnation, so that all progen, born of himself and 'his wife. . . should draw to itself original sin, and thence be drawn through diverse errors and pains to that last and endless torture with the angels, who deserted and corrupted (others), and with those who inherit and share in their portion."
Augustine's exposition of the doctrine exercised a great and lasting influence throughout the subsequent centuries, and has been, in its broader outlines, followed by the theologians of the Middle Ages. A more definite and scientific formulation grew up with the development of the stricter methods of scholastic philosophy, which reached its complete expansion in the 13th century.
Thomas Aquinas, the greatest theologian of the scholastic period, declares that the essence of original sin consists in the "privation of original justice, and understanding by original justice that state in which Adam was created and lived prior to the fall, with all the gifts of grace which God had bestowed upon him with the view to his supernatural end in ultimate possession of the Divine Vision. All this Adam forfeited when he fell, and that forfeiture passed by natural generation to all his descendants. In this view original sin is not a positive evil added to human nature, but the deprivation of a supernatural good originally bestowed upon the race in the headship of Adam. Following this original loss, as a penalty of Adam's transgression, came the direful consequences of death, the confusion and disorders of all the human faculties, and the sting of concupiscence. This is the accepted teaching of the Roman Catholic Church, and the Council of Trent defines as of faith, that Adam lost original justice, not only for himself, but also for us; that he poured sin, which is the death of the soul, into the whole human race, and that this sin comes, not by imitation of Adam's transgression, but by propagation from him.
The reformers of the 16th century generally held to a very strict interpretation of the Augustinian view, and regarded original sin as a complete corruption of the will and reason. Luther held that it consisted in concupiscence. The Lutheran and the Reformed churches both held similar views regarding original sin, following Calvin rather than Zwingli, who looked upon it as an evil or disease, and only as a sin when a commandment was thereby transgressed. The Arminians and Socinians, on the other hand, discountenanced the ecclesiastical view of the doctrine. While the Protestant Church maintained that Jesus alone was absolutely free from original sin, the Roman Catholic Church exempts the Virgin Mary from its dominion. Uniform adhesion to the Augustinian dogma on the part of the reformers was by no means the case. From Luther's dispute with Erasmus, who would only admit a weakness of the freewill and not its destruction, up to the present time the doctrine has been variously defended and attacked, philosophers as well as theologians taking part in the controversy. Kant showed the moral signification of the doctrine, and represented original sin as an inherent tendency in man's nature to evil. Rationalism, on the other hand, taught with Pelagius that it was only a weakness of man's nature with regard to knowledge and his power for good.
In recent times most orthodox theologians, such as Olshausen, Hengstenberg and others, have stood up for the Augustinian doctrine, while those of the liberal school have modified it in various ways.