Anti-pelagian Writings by St. Augustine
Chapter 20 [XIX.]--How a Man Makes a Good or a Bad Tree.
Now a man makes a good tree when he receives the grace of God. For it is not by himself that he makes himself good instead of evil; but it is of Him, and through Him, and in Him who is always good. And in order that he may not only be a good tree, but also bear good fruit, it is necessary for him to be assisted by the self-same grace, without which he can do nothing good. For God Himself cooperates in the production of fruit in good trees, when He both externally waters and tends them by the agency of His servants, and internally by Himself also gives the increase. A man, however, makes a corrupt tree when he makes himself corrupt, when he falls away from Him who is the unchanging good; for such a declension from Him is the origin of an evil will. Now this decline does not initiate some other corrupt nature, but it corrupts that which has been already created good. When this corruption, however, has been healed, no evil remains; for although nature no doubt had received an injury, yet nature was not itself a blemish.