The origin of the heresy known as the sinful nature is from Augustine.
Augustine forsook his position on free will, saying “I have tried hard to maintain the free choice of the human will, but the grace of God prevailed,”49 he began to influence the rest of the Church with the idea of natural inability, which view the Church did not previously believe at all. The doctrine of free will was soon replaced with the idea of a ruined, corrupt, sinful nature.
Regarding the doctrine of a sinful nature, Charles Finney said, “This doctrine is a stumbling-block both to the church and the world, infinitely dishonorable to God, and an abomination alike to God and the human intellect, and should be banished from every pulpit, and from every formula of doctrine, and from the world. It is a relic of heathen philosophy, and was foisted in among the doctrines of Christianity by Augustine, as everyone may know who will take the trouble to examine for himself.”50
Harry Conn said, “Augustine, after studying the philosophy of Manes, the Persian philosopher, brought into the church from Manichaeism the doctrine of original sin.”51
The corruption of our nature, or the loss of our free will, Augustine credited to the original sin of Adam. Augustine said that the “free choice of the will was present in that man who was the first to be formed… But after he sinned by that free will, we who have descended from his progeny have been plunged into necessity.”52 “By Adam’s transgression, the freedom of’ the human will has been completely lost.”53 “By the greatness of the first sin, we have lost the freewill to love God.” And finally he said, “by subverting the rectitude in which he was created, he is followed with the punishment of not being able to do right” and “the freedom to abstain from sin has been lost as a punishment of sin.”54
See the historical facts in the early church below on free will and sinful nature.