John Chrysostom: Tree of Knowledge of Good and Evil Provided More Clear Knowledge

Let us hold on to that fact, then, that obedience is good and disobedience evil, and we shall thus understand the former case as well. The tree is referred to as the knowledge of good and evil, in fact, for the reason that the commandment exercising them in obedience and disobedience was given in regard to the tree: while Adam knew before this that obedience was good and disobedience evil, he learnt it more clearly later from actual experience.

- John Chrysostom (around A.D. 347 to around A.D. 407), Sermon 7 on Genesis, in St. John Chrysostom, Eight Sermons on the Book of Genesis, p. 116 (2004), Robert C. Hill translator.