Taken from Peri Archon (De Principiis) I.2.8:
'But since He is called by the apostle not only the brightness of His glory, but also the express figure of His person or subsistence, it does not seem idle to inquire how there can be said to be another figure of that person besides the person of God Himself, whatever be the meaning of person and subsistence. Consider, then, whether the Son of God, seeing He is His Word and Wisdom, and alone knows the Father, and reveals Him to whom He will (i.e., to those who are capable of receiving His word and wisdom), may not, in regard of this very point of making God to be understood and acknowledged, be called the figure of His person and subsistence; that is, when that Wisdom, which desires to make known to others the means by which God is acknowledged and understood by them, describes Himself first of all, it may by so doing be called the express figure of the person of God. In order, however, to arrive at a fuller understanding of the manner in which the Saviour is the figure of the person or subsistence of God, let us take an instance, which, although it does not describe the subject of which we are treating either fully or appropriately, may nevertheless be seen to be employed for this purpose only, to show that the Son of God, who was in the form of God, divesting Himself (of His glory), makes it His object, by this very divesting of Himself, to demonstrate to us the fullness of His deity. For instance, suppose that there were a statue of so enormous a size as to fill the whole world, and which on that account could be seen by no one; and that another statue were formed altogether resembling it in the shape of the limbs, and in the features of the countenance, and in form and material, but without the same immensity of size, so that those who were unable to behold the one of enormous proportions, should, on seeing the latter, acknowledge that they had seen the former, because it preserved all the features of its limbs and countenance, and even the very form and material, so closely, as to be altogether undistinguishable from it; by some such similitude, the Son of God, divesting Himself of His equality with the Father, and showing to us the way to the knowledge of Him, is made the express image of His person: so that we, who were unable to look upon the glory of that marvellous light when placed in the greatness of His Godhead, may, by His being made to us brightness, obtain the means of beholding the divine light by looking upon the brightness. This comparison, of course, of statues, as belonging to material things, is employed for no other purpose than to show that the Son of God, though placed in the very insignificant form of a human body, in consequence of the resemblance of His works and power to the Father, showed that there was in Him an immense and invisible greatness, inasmuch as He said to His disciples, "He who sees Me, sees the Father also;" and, "I and the Father are one." And to these belong also the similar expression, "The Father is in Me, and I in the Father."'