On Christ
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.”
9. Let us see now what is the meaning of the expression which is found in the Wisdom of Solomon, where it is said of Wisdom that “it is a kind of breath of the power of God, and the purest efflux of the glory of the Omnipotent, and the splendour of eternal light, and the spotless mirror of the working or power of God, and the image of His goodness.” These, then, are the definitions which he gives of God, pointing out by each one of them certain attributes which belong to the Wisdom of God, calling wisdom the power, and the glory, and the everlasting light, and the working, and the goodness of God. He does not say, however, that wisdom is the breath of the glory of the Almighty, nor of the everlasting light, nor of the working of the Father, nor of His goodness, for it was not appropriate that breath should be ascribed to any one of these; but, with all propriety, he says that wisdom is the breath of the power of God. Now, by the power of God is to be understood that by which He is strong; by which He appoints, restrains, and governs all things visible and invisible; which is sufficient for all those things which He rules over in His providence; among all which He is present, as if one individual. And although the breath of all this mighty and immeasurable power, and the vigour itself produced, so to speak, by its own existence, proceed from the power itself, as the will does from the mind, yet even this will of God is nevertheless made to become the power of God.
Another power accordingly is produced, which exists with properties of its own—a kind of breath, as Scripture says, of the primal and unbegotten power of God, deriving from Him its being, and never at any time non-existent. For if any one were to assert that it did not formerly exist, but came afterwards into existence, let him explain the reason why the Father, who gave it being, did not do so before. And if he shall grant that there was once a beginning, when that breath proceeded from the power of God, we shall ask him again, why not even before the beginning, which he has allowed; and in this way, ever demanding an earlier date, and going upwards with our interrogations, we shall arrive at this conclusion, that as God was always possessed of power and will, there never was any reason of propriety or otherwise, why He may not have always possessed that blessing which He desired. By which it is shown that that breath of God's power always existed, having no beginning save God Himself. Nor was it fitting that there should be any other beginning save God Himself, from whom it derives its birth. And according to the expression of the apostle, that Christ “is the power of God,” it ought to be termed not only the breath of the power of God, but power out of power.
Source: De Principiis (New Advent)