Concerning the Nature of Good, Against the Manichæans

Likewise because sin, or unrighteousness, is not the striving after evil nature but the desertion of better, it is thus found written in the Scriptures: "Every creature of God is good." And accordingly every tree also which God planted in Paradise is assuredly good. Man did not therefore strive after an evil nature when he touched the forbidden tree; but by deserting what was better, he committed an evil deed. Since the Creator is better than any creature which He has made, His command should not have been deserted, that the thing forbidden, however good, might be touched; since the better having been deserted, the good of the creature was striven for, which was touched contrary to the command of the Creator. God did not plant an evil tree in Paradise; but He Himself was better who prohibited its being touched.