TWH: I would first recommend that a person do a study in which they trace the places where God's glory is seen in the Old and New Testaments. Trust me, it is a wonderful study. Regarding John 17:22–25, we need to put this into context. Clearly, the glory is something different than what is generally meant when we hear people talking about the glory of God in Christian circles. Jesus, for example, in 17:5 says that he wishes to be glorified with the Father and with the glory that he had (*note that it does not say "has" at this point, before Jesus is resurrected) with the Father before the world was [and which they experienced up until the incarnation]. There are a number of different passages in John that deal with the glory. First, John 1, where John mentions that "we" beheld his glory. When John says that, he is referring to Peter, James, and himself (referring to when Jesus is transfigured; see Matthew 17). Then there is the reference in John 12 to Isaiah seeing Jesus' glory (in Isaiah 6). This is completely different, both of these examples, from anything that anyone has seen or experienced in the body of Christ. What I can say about what Jesus prays in John 17:22 is this––two points:
1. Christians, like creation, proclaim the glory of God (which is to say, they declare his greatness and his supreme value) when they are one like he and the Father are one.
2. Though Christians have not seen his glory––yet––the New Testament is clear that they will.This is one of the most amazing promises of eternal life. Believers will behold his glory. Jude specifically mentions that they will stand in the presence of his glory with great joy (Jude 24). Contrast this to 2 Thess. 1:9, which reads, "These will pay the penalty of eternal destruction, away from the presence of the Lord and from the glory of his power." One of the worst parts about hell is someone will miss out on seeing the glory of God. And one of the best parts about heaven will be seeing it. That's my short answer. I hope it helps. I do not believe believers have seen the glory of God (both John and Peter mention seeing it) and they should discuss his glory appropriately by not minimizing the experience. They will see it––one day––but they have not seen it––yet. Jesus' promise is that they will. Before taking John 17:22 as support for the position that more than Peter, James, and John had witnessed the glory of God personally during Jesus' ministry, consider what Jesus prays just two verses later: "Father, I desire that they also, whom you have given me, will be with me where I am, so that they may see my glory, which you have given me" (John 17:24). It seems clear in my opinion that what Jesus meant in v. 22 is different than the request in v. 24. To see the glory necessitates being in the presence of God, as Jesus says, where he is.