10 Recognize in yourself something which I wish to say within, in yourself; not within as if in your body, for in a sense one may say, “in yourself.” For there is in you health, your age whatever it be, but this in regard to the body. In you is your hand and your foot; but there is one thing in you, within; another thing in you as in your garment. But leave outside your garment and yourself, descend into yourself, go to your secret place, your mind, and there see, if you can, what I wish to say.
For if you are far from yourself, how can you come near to God? I was speaking of God, and you believed that you would understand. I am speaking of the soul, I am speaking of yourself: understand this, there I will try you. For I do not travel very far for examples, when I mean to give you some similitude to your God from your own mind; because surely not in the body, but in that same mind, was man made after the image of God. Let us seek God in His own similitude; let us recognize the Creator in His own image.
There within, if we can, let us find this that we speak of—how the Father shows to the Son, and how the Son sees what the Father shows, before anything is made by the Father through the Son. But when I shall have spoken, and you have understood, you must not think that spoken of to be something just such as our example, that you may therein keep piety, which I wish to be kept by you, and earnestly admonish you to keep: that is, if you are not able to comprehend what God is, do not think it a small matter for you to know what He is not.
Source: Tractates on the Gospel of John (New Advent)