My prayer is not for them alone. I pray also for those who will believe in me through their message, that all of them may be one, Father, just as you are in me and I am in you. May they also be in us so that the world may believe that you have sent me. I have given them the glory that you gave me, that they may be one as we are one — I in them and you in me — so that they may be brought to complete unity. Then the world will know that you sent me and have loved them even as you have loved me. (John 17:20-23)
The Father, Son and Holy Spirit, though they are three in number, yet they are one in nature, one in substance. They dwell in each other, participate in each other, have intimate fellowship with each other. The early Church Fathers thought deeply about these things and theologians have referred to the mutual fellowship and participation of the Three as perichoresis, the interweaving of Father, Son and Holy Spirit in a sort of divine choreography.
The Three are glorified with the same glory, which is the greatness of their goodness revealed. In his divinity, the eternal Son of God always possessed this glory, but in his humanity, which happened in time, this glory was given to him.
The Three also love with the same love. There is only one love, for God is love and God is one. And it is out of the abundance of their love for each other that the world and humanity came into being.
In the garden of Gethsemane on the night before he was crucified, Jesus prayed for the same unity for his disciples, and all who believe through them, that we may all be one. This is not only unity with each other but also with God — for there is no unity apart from God, who alone is one.
Just as the Father is in Jesus the Son, and Jesus is in the Father, so Jesus prayed that we may be in the Father and the Son. Jesus is in us just as the Father is in him. We are in the Father, Son and Spirit, and they are in us. So we are taken up into the divine interweaving of their fellowship.
The glory Jesus received from the Father is the same glory he shared with the Father before the world began (John 17:5). This is the glory he gives to us, so that we may be one, just as the Father and Son are one. It is a complete unity that Jesus prays for us, for the love the Father has for us is the same love he has for Jesus — love itself is one and cannot be divided.
The Church always confesses the mystery of the Trinity: One God, three Persons. And though Jesus has two natures, fully human and fully divine, we confess that these natures are perfectly united in one person. The unity Jesus prays for his disciples is the unity — the wholeness — of the Three and of Jesus in his divine and human natures.
The truth about all who are in Christ is that, though we be many in number, yet we are one. We are one body, and though the body has many members, yet it is still one body — the body of Christ. This unity is not something we must somehow accomplish for ourselves — it has already been done by Christ himself — but we must learn to live out this oneness by the power of the Holy Spirit.
As a prisoner for the Lord, then, I urge you to live a life worthy of the calling you have received. Be completely humble and gentle; be patient, bearing with one another in love. Make every effort to keep the unity of the Spirit through the bond of peace. There is one body and one Spirit, just as you were called to one hope when you were called; one Lord, one faith, one baptism; one God and Father of all, who is over all and through all and in all. (Ephesians 4:1-6)The unity we have with each other is the same unity we have with the Father, through the Son and by the Holy Spirit. Thus we partake of and participate in the divine nature (2 Peter 1:4). What God is in his own being, he shares with us in grace. It is given to us so that we may enjoy fellowship with the Father, Son and Spirit, the same fellowship they have always enjoyed together with each other from before the world began. This unity is all-encompassing and is why Jesus came.
For God was pleased to have all his fullness dwell in him, and through him to reconcile to himself all things, whether things on earth or things in heaven, by making peace through his blood, shed on the cross. (Colossians 1:19-20)In the end, heaven and earth, though they be two, shall be fully and completely one. And God shall be all in all. The eternal unity of the Father, Son and Holy Spirit shall prevail in everything.