7 But to this opinion, which I certainly do not see to be conformable to the truth, there is nothing to urge us, if, when the Son says, “And now, O Father, glorify Thou me with Your own self, with the glory which I had with You before the world was,” we understand the predestination of the glory of His human nature, as thereafter, from being mortal, to become immortal with the Father: and that this had already been done by predestination before the world was, as also in its own time it was done in the world.
For if the apostle has said of us, “According as He has chosen us in Him before the foundation of the world,” why should it be thought incongruous with the truth, if the Father glorified our Head at the same time as He chose us in Him to be His members? For we were chosen in the same way as He was glorified; inasmuch as before the world was, neither we nor the Mediator between God and men, the man Christ Jesus, were yet in existence. But He who, in as far as He is His Word, of His own self “made even those things which are yet to come,” and “calls those things which are not as though they were,” certainly, in respect of His manhood as Mediator between God and men, was Himself glorified on our behalf by God the Father before the foundation of the world, if it be so that we also were then chosen in Him.
For what says the apostle? “And we know that all things work together for good to them that love God, to them who are the called according to His purpose. For whom He did foreknow, He also did predestinate to be conformed to the image of His Son, that He might be the first-born among many brethren: and whom He did predestinate, them He also called.”
Source: Tractates on the Gospel of John (New Advent)