49 It is therefore for the promotion of us, the assumed humanity, that God shall be all in all. He Who was found in the form of a servant, though He was in the form of God, is now again to be confessed in the glory of God the Father: that is, without doubt He dwells in the form of God, in Whose glory He is to be confessed. All is therefore a dispensation only, and not a change of His nature; for He abides still in Him, in Whom He ever was. But there intervenes a new nature, which began in Him with His human birth, and so all that He obtains is on behalf of that nature which before was not God, since after the Mystery of the Dispensation God is all in all.
It is, therefore, we who are the gainers, we who are promoted, for we shall be conformed to the glory of the body of God. Further the Only-begotten God, despite His human birth, is nothing less than God, Who is all in all. That subjection of the body, by which all that is fleshly in Him, is swallowed up into the spiritual nature, will make Him to be God and all in all, since He is Man also as well as God; and His humanity which advances towards this goal is ours also. We shall be promoted to a glory conformable to that of Him Who became Man for us, being renewed unto the knowledge of God, and created again in the image of the Creator, as the Apostle says, Having put off the old man with his doings, and put on the new man, which is being renewed unto the knowledge of God, after the image of Him that created him. Thus is man made the perfect image of God.
For, being conformed to the glory of the body of God, he is exalted to the image of the Creator, after the pattern assigned to the first man. Leaving sin and the old man behind, he is made a new man unto the knowledge of God, and arrives at the perfection of his constitution, since through the knowledge of his God he becomes the perfect image of God. Through godliness he is promoted to immortality, through immortality he shall live for ever as the image of his Creator.
Source: On the Trinity (New Advent)