5 In a way similar, also, to this, He proceeds to say: “And now, O Father, glorify me with Your own self with the glory which I had with You before the world was.” For He had said above, “Father, the hour has come; glorify Your Son, that Your Son may glorify You:” in which arrangement of the words He had shown that the Father was first to be glorified by the Son, in order that the Son might glorify the Father. But now He said, “I have glorified You on the earth: I have finished the work which You gave me to do; and now glorify Thou me;” as if He Himself had been the first to glorify the Father, by whom He then demands to be glorified.
We are therefore to understand that He used both words above in accordance with that which was future, and in the order in which they were future, “Glorify Your Son, that Your Son may glorify You:” but that He now used the word in the past tense of that which was still future, when He said, “I have glorified You on the earth: I have finished the work which You gave me to do.” And then, when He said, “And now, O Father, glorify Thou me with Your own self,” as if He were afterwards to be glorified by the Father, whom He Himself had first glorified; what did He intimate but that, when He said above, “I have glorified You on the earth,” He had so spoken as if He had done what He was still to do; but that here He demanded of the Father to do that whereby the Son should yet do so; in other words, that the Father should glorify the Son, by means of which glorification of the Son, the Son also was yet to glorify the Father?
In fine, if, in connection with that which was still future, we put the verb also in the future tense, where He has used the past in place of the future tense, there will remain no obscurity in the sentence: as if He had said, “I will glorify You on the earth: I will finish the work which You have given me to do; and now, O Father, glorify Thou me with Your own self.” In this way it is as plain as when He says, “Glorify Your Son, that Your Son may glorify You:” and this is indeed the whole sentence, save that here we are told also the manner of that same glorification, which there was left unnoticed; as if the former were explained by the latter to those whose hearts it was able to stir, how it was that the Father should glorify the Son, and most of all how the Son also should glorify the Father.
For in saying that the Father was glorified by Himself on the earth, but He Himself by the Father with the Father's very self, He showed them assuredly the manner of both glorifications. For He Himself glorified the Father on earth by preaching Him to the nations; but the Father glorified Him with His own self in setting Him at His own right hand. But on that very account, when He says afterward in reference to the glorifying of the Father, “I have glorified You,” He preferred putting the verb in the past tense, in order to show that it was already done in the act of predestination, and what was with perfect certainty yet to take place was to be accounted as already done; namely, that the Son, having been glorified by the Father with the Father, would also glorify the Father on the earth.
Source: Tractates on the Gospel of John (New Advent)