And now, Father, you glorify me at your side with the glory that I had at your side before the world existed. (John 17:5, Lexham Bible)
John 17:5 is a strong witness for the personal pre-existence of Jesus. For articles on this blog addressing this verse and various Christologies (e.g., those of Christadelphians such as Duncan Heaster and Dave Burke) that reject personal pre-existence in favour of notional pre-existence merely, see:
Oneness Pentecostal theologian and apologist David Bernard wrote the following about John 17:5 defending the claim the verse is speaking of Jesus notionally pre-existing in the “mind” of God (like how a car “pre-exists” notionally in the mind of an engineer):
In John 17:5 Jesus prayed, “O Father, glorify thou me with thine own self with the glory which I had with thee before the world was.” Again, Jesus spoke of the glory He had as God in the beginning and the glory the Son had in the plan and mind of God. It would not mean that Jesus pre-existed with the glory as the Son. Jesus was praying, so He must have been speaking as a man and not as God. We know that humanity did not pre-exist the Incarnation, so Jesus was talking about the glory the Son had in the plan of God from the beginning. (David K. Bernard, the Oneness of God [Series in Pentecostal Theology, Volume 1; Hazelwood, Miss.: 1983], 183-84)
In a recent book critiquing Oneness Pentecostalism from a Catholic perspective, Mark McNeil, a former Oneness advocate, wrote the following in response to Bernard’s (eisegetical) reading of John 17:5:
Bernard assumes that “prayer” is incompatible with the apparent sense of John 17:5, and therefore an alternative explanation must be sought. He is caught in a strange situation, however, since Jesus obviously speaks about divine glory and yet distinguishes his experience of that glory from the Father’s. Bernard covers both these facts by saying that Jesus longed for return to his glory “as God,” but also to the glory he had as God’s plan. For Bernard, two basically different “glories” are in view. This is needless and unjustified. The Son’s glory with the Father must be divine glory. Placing himself alongside the Father supports the divinity of both Father and Son. The “plan” of God, however, cannot be equated with God. Elsewhere Bernard will place God’s eternal love for Jesus in the same category as God’s love for the Church. If both God’s Son and the Church are parts of the divine “plan,” why is not equated with divine preexistent glory and the other is not? Is the Church “God” since it is part of God’s eternal purposes and, using Bernard’s logic, “with” God in his plan before the worlds were made?
If we grant that the Father and Son stand in an eternal relationship toward each other, a relationship characterized by love, communication between them is a given. That the Son of God in his incarnate humanity expresses himself toward the Father in prayer is not a contradiction but is, rather, what we would expect if such a relationship truly exists. Surely there are features of Jesus’ prayers that arise from his human nature, but the fundamental union that exists between the Father and the Son is the root of that communication. The prayers of Jesus in time, in the context of his human journey, reveal a life of communion and love that infinitely transcends his immediate human context. John 17:5, and other similar texts, display, by their bursts of insight into the eternal life of God, this infinite transcendence. (Mark A. McNeil, All in the Name: How the Bible Led Me to Faith in the Trinity and the Catholic Church [El Cajon, Calif.: Catholic Answers Press, 2018], 89-90, italics in original)