6 For in this the proud soul has passed bounds, and, in a manner, become avaricious. For, “The root of all evils is avarice;” and again it is said, “The beginning of all sin is pride.” And we ask, it may be, how these two sentences agree: “The root of all evils is avarice;” and, “The beginning of all sin is pride.” If pride is the beginning of all sin, then is pride the root of all evils. Now certainly, “the root of all evils is avarice.” We find that in pride there is also avarice, (or grasping;) for man has passed bounds: and what is it to be avaricious to go beyond that which suffices.
Adam fell by pride: “the beginning of all sin is pride,” says it: did he fall by grasping? What more grasping, than he whom God could not suffice? In fact, my brethren, we read how man was made after the image and likeness of God: and what said God of him? “And let him have power over the fishes of the sea, and over the fowl of the heaven, and over all cattle which move upon the earth.” Said He, Have power over men? “Have power,” says He: He has given him natural power: “have power” over what?
“over the fishes of the sea, the fowl of the heaven, and all moving things which move upon the earth.” Why is this power over these things a natural power? Because man has the power from this; that he was made after the image of God. And in what was he made after God's image? In the intellect, in the mind, in the inner man; in that he understands truth, distinguishes between right and wrong, knows by whom he was made, is able to understand his Creator, to praise his Creator: he has this intelligence, who has prudence.
Therefore when many by evil lusts wore out in themselves the image of God, and by perversity of their manners extinguished the very flame, so to say, of intelligence, the Scripture cried aloud to them, “Become not ye as the horse and mule which have no understanding.” That is to say, I have set you above the horse and mule; you, I made after my image, I have given you power over these. Why? Because they have not the rational mind: but you by the rational mind art capable of truth, understandest what is above you: be subject to Him that is above you, and beneath you shall those things be over which you were set. But because by sin man deserted Him whom he ought to be under, he is made subject to the things which he ought to be above.
Source: Homilies on the First Epistle of John (New Advent)