I hope that all is well with you, and a good afternoon. Always nice to hear from you.
Marcos, I don't see the "Deity" of Christ in John 17:5 either, nor do I discern here his literal and eternal existence with God prior to his "Incarnation.". John 17:5 is an example of prolepsis, which Jesus invoked often in the 17th chapter of John. You may be surprised that some prominent Trinitarians also find no evidence for Christ's eternal existence in this particular verse. Here's St. Augustine:
5. In a way similar, also, to this, He proceeds to say: “And now, O Father, glorify thou me with Thine own self with the glory which I had with Thee before the world was.” For He had said above, “Father, the hour is come; glorify Thy Son, that Thy Son may glorify Thee:” 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 Thee on the earth: I have finished the work which Thou gavest 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 Thy Son, that Thy Son may glorify Thee:” but that He now used the word in the past tense of that which was still future, when He said, “I have glorified Thee on the earth: I have finished the work which Thou gavest me to do.” And then, when He said, “And now, O Father, glorify Thou me with Thine 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 Thee 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 Thee on the earth: I will finish the work which Thou hast given me to do; and now, O Father, glorify Thou me with Thine own self.” In this way it is as plain as when He says, “Glorify Thy Son, that Thy Son may glorify Thee:” 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 Thee,” 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.
6. But this predestination He still more clearly disclosed in respect of His own glorification, wherewith He was glorified by the Father, when He added, “With the glory which I had, before the world was, with Thee.” The proper order of the words is, “which I had with Thee before the world was.” To this apply His words, “And now glorify Thou me;” that is to say, as then, so also now: as then, by predestination; so also now, by consummation: do Thou in the world what had already been done with Thee before the world: do in its own time what Thou hast determined before all times. This, some have imagined, should be so understood as if the human nature, which was assumed by the Word, were converted into the Word, and the man were changed into God; yea, 398were we reflecting with some care on the opinions they have advanced, as if the humanity were lost in the Godhead. For no one would go the length of saying that out of such a transmutation of the humanity the Word of God is either doubled or increased, so that either what was one should now be two, or what was less should now be greater. Accordingly, if with His human nature changed and converted into the Word, the Word of God will still be as great as He was, and what He was, where is the humanity, if it is not lost?
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 Thine own self, with the glory which I had with Thee 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 hath chosen us in Him before the foundation of the world,”1709 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,1710 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 “calleth those things which are not as though they were,”1711 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 saith 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.”1712
8. But perhaps we shall have some fear in saying that He was predestinated, because the apostle seems to have said so only in reference to our being made conformable to His image. As if, indeed, any one, faithfully considering the rule of faith, were to deny that the Son of God was predestinated, who yet cannot deny that He was man. For it is rightly said that He was not predestinated in respect of His being the Word of God, God with God. For how could He be predestinated, seeing He already was what He was, without beginning and without ending, everlasting? But that, which as yet was not, had to be predestinated, in order that it might come to pass in its time, even as it was predestinated so to come before all times. Accordingly, whoever denies predestination of the Son of God, denies that He was also Himself the Son of man. But, on account of those who are disputatious, let us also on this subject listen to the apostle in the exordium of his epistles. For both in the first of his epistles, which is that to the Romans, and in the beginning of the epistle itself, we read: “Paul, a servant of Jesus Christ, called [to be] an apostle, separated unto the gospel of God, which He had promised afore by His prophets in the Holy Scriptures, concerning His Son, who was made for Him of the seed of David according to the flesh, who was predestinated1713 the Son of God in power, according to the Spirit of holiness, by the resurrection from the dead.”1714 In respect, then, of this predestination also, He was gloried before the world was, in order that His glory might be, by the resurrection from the dead, with the Father, at whose right hand He sitteth. Accordingly, when He saw that the time of this, His predestinated glorification, was now come, in order that what had already been done in predestination might also be done now in actual accomplishment, He said in His prayer, “And now, O Father, glorify Thou me with Thine own self with the glory which I had with Thee before the world was:” as if He had said, The glory which I had with Thee, that is, that glory which I had with Thee in Thy predestination, it is time that I should have with Thee also in sitting at Thy right hand. But as the discussion of this question has already kept us long, what follows must be taken into consideration in another discourse.