Augustine of Hippo, On Nature and Grace Chapter 34: A Man’s Sin is His Own, But He Needs Grace for His Cure

Well, but what does he mean when he says: “Then again, how can one be subjected to God for the guilt of that sin, which he knows is not his own? For,” says he, “his own it is not, if it is necessary. Or, if it is his own, it is voluntary: and if it is voluntary, it can be avoided.” We reply: It is unquestionably his own. But the fault by which sin is committed is not yet in every respect healed, and the fact of its becoming permanently fixed in us arises from our not rightly using the healing virtue; and so out of this faulty condition the man who is now growing strong in depravity commits many sins, either through infirmity or blindness. Prayer must therefore be made for him, that he may be healed, and that he may thenceforward attain to a life of uninterrupted soundness of health; nor must pride be indulged in, as if any man were healed by the self-same power whereby he became corrupted.