Luke 6:45

(Hom. 9, in Hexameron.) In truth, self knowledge seems the most important of all. For not only the eye, looking at outward things, fails to exercise its sight upon itself, but our understanding also, though very quick in apprehending the sin of another, is slow to perceive its own defects.

The quality of the words shows the heart from which they proceed, plainly manifesting the inclination of our thoughts. Hence it follows, For out of the abundance of the heart the mouth speaketh.

(Hom. 42. in Matt.) For it is a natural consequence when wickedness abounds within, that wicked words are breathed as far as the mouth; and therefore when you hear of a man uttering abominable things, do not suppose that there lies only so much wickedness in him as is expressed in his words, but believe the fountain to be more copious than the stream.

But having shown that the good and the bad man may be discerned by their works as a tree by its fruits, he now sets forth the same thing by another figure, saying, A good man out of the good treasure of his heart bringeth forth that which is good, and the evil man out of the evil treasure bringeth forth that which is evil.

The treasure of the heart is the same as the root of the tree. He therefore who has in his heart the treasure of patience and perfect love, brings forth the best fruits, loving his enemy, and doing the other things which have been taught above. But he who keeps a bad treasure in his heart does the contrary to this.