40 In His body, the same body though now made glorious, He reigns until the authorities are abolished, death conquered, and His enemies subdued. This distinction is carefully preserved by the Apostle: the authorities and powers are abolished, the enemies are subjected. Then, when they are subjected, He, that is the Lord, shall be subjected to Him that subjects all things to Himself, that God may be all in all, the nature of the Father's divinity imposing itself upon the nature of our body which was assumed.
It is thus that God shall be all in all: according to the Dispensation He becomes by His Godhead and His manhood the Mediator between men and God, and so by the Dispensation He acquires the nature of flesh, and by the subjection shall obtain the nature of God in all things, so as to be God not in part, but wholly and entirely. The end of the subjection is then simply that God may be all in all, that no trace of the nature of His earthly body may remain in Him. Although before this time the two were combined within Him, He must now become God only; not, however, by casting off the body, but by translating it through subjection; not by losing it through dissolutions, but by transfiguring it in glory: adding humanity to His divinity, not divesting Himself of divinity by His humanity.
And He is subjected, not that He may cease to be, but that God may be all in all, having, in the mystery of the subjection, to continue to be that which He no longer is, not having by dissolution to be robbed of Himself, that is, to be deprived of His being.
Source: On the Trinity (New Advent)