Jesus is praying for us, who have believed in him because of the apostle's message we have read or heard talked about. His prayer is for our complete unity, because such unity shows the world that Jesus truly came from God. We are so prone to division that when people see us acting in unity there can be only one explanation - we are united by Jesus, and he must have come from God to produce such a miracle (vs 21,23)!
The unity Jesus prays for is not brought about by our becoming clones of each other. Jesus and the Father are in perfect unity, yet they are not identical. Jesus and the Father are one in that they are 'in' each other, somehow included in each other's actions. So Paul can say, 'God was in Christ reconciling the world to himself' (2 Corinthians 5:19). Jesus constantly said that he did what he saw the Father doing, and spoke what his Father told him to say. He told his disciples that if they had seen him they had seen the Father (John 14:9,10). He told them that he and the Father would make their home with those who love and obey him (14:23). Now Jesus prays that we might be in the Father and him (17:21), and that he might be in us (v.23).
What does it mean to be 'in the Father', or 'in Christ'? Paul says, 'Your life is now hidden with Christ in God' (Colossians 3:3). There is a kind of unity which is spiritual and mysterious (theologians call it a 'mystical union'), but which is real and very important; it is the foundation of our Christian life. Through faith in Jesus we have become spiritually united with him in such a way that all the benefits of his life and death and resurrection, and of his position and relationship with God, become ours also. Jesus is spiritually united with God - therefore we are too. Paul says that our new life is bound up with Jesus' resurrection life, and his life is bound up with God's life, and this is so real that when the time comes for Jesus to be revealed in all his glory at the end of time, we will be revealed in glory as well - we're bound together! (Colossians 3:4.) So we are in the Son, and in the Father, through our belief in the message of the apostles. It is this unity with God through Jesus that is the source of the unity with each other for which Jesus is praying.
Such unity has to be visible to have any effect on the world. Our unity from God becomes visible when we take God's purposes as our purposes, God's ways as our ways, and especially God's love as our love. Love beyond telling was the glory God gave Christ (v.22, 12:23-26), greater than all position and majesty; that glory is given us, too. We can love unreservedly when we know God has loved us unreservedly - and the world will see, and it too will know that God loves us (v.23).
Jesus prays in v.24 that we might see his glory in all its perfection in the presence of God. In v.5 he had prayed for God to give back to him his original glory, the majesty and beauty he had before the world was created; he wants us to see that also, in addition to the glory of his love. At present we see with the eyes of faith; one day we will see in God's presence. The vision of Christ in all his glory will be utterly fulfilling; any pleasure in our own happiness will be negligible in comparison with our pleasure in him!
Back to the present: we are still in process! We know that Jesus came from God; through him we are beginning to get to know God, and will continue to know him better. The more we know of God, the more we will know of his love, and of the loving presence of Jesus in us through his Spirit (1 John 4:13).
ISSUES AND QUESTIONS
It is easy to show our diversity as Christians; how can we show our unity? How important is our unity to us?
IDEAS FOR MEETINGS
What is the most beautiful sight you have ever seen?
Give out pens and paper to the group. Read Revelation 1:12-16, John's vision of Christ. Then ask the members each to write (or draw) their own vision of Christ in glory - using as much or as little symbolism as they like. When all have finished, let each read or show their efforts in turn. Afterwards read verses 17 and 18. Respond in praise.