Jumping in a little late but I thought it was worth a try. I'm not trying to convince anyone to believe what I believe, I have plenty of doubt lately, I just thought I would post some thoughts on the passages quoted.
"... That they all may be one, as thou, Father, in me, and I in thee; that they also may be one in us ... that they may be one, as we also are one: I in them, and thou in me; that they may be made perfect in one ... Father, I will that where I am, they also whom thou hast given me may be with me; that they may see my glory which thou hast given me, because thou hast loved me before the creation of the world..." (John 17:11, 21-24)
If we back it up we can see that Jesus is not praying for the world but only for believers to be one (v.9) and that Christians are kept from falling away from the Christian faith (v.12). Jesus also reveals that one was lost on purpose or with a purpose and that was to fulfil scripture. Jesus is praying that his people, believers or Christians continue in his teachings (v.15-20) in the world and use them when dealing with the world. (kosmos has seven different meanings depending on the context) The world in the New Testament often meant those who are outside of the faith group. Jews referred to the 'world' in reference to gentiles. Jesus uses the 'world' in reference to unbelievers or non Christians. Jesus is praying that his people interact with the world with one mind. In unity.
"So we being many, are one body in Christ... " Romans 12:5
Paul lays the foundation for this quote in Romans 8:
12 So then, brothers, we are debtors, not to the flesh, to live according to the flesh. 13 For if you live according to the flesh you will die, but if by the Spirit you put to death the deeds of the body, you will live. 14 For all who are led by the Spirit of God are sons[f] of God. 15 For you did not receive the spirit of slavery to fall back into fear, but you have received the Spirit of adoption as sons, by whom we cry, “Abba! Father!” 16 The Spirit himself bears witness with our spirit that we are children of God, 17 and if children, then heirs—heirs of God and fellow heirs with Christ, provided we suffer with him in order that we may also be glorified with him.
Jesus mentions this teaching throughout the Gospels and Paul confirms this in his Epistles. When a person comes to faith it is through regeneration or being 'born again.' At this point we are given the Holy Spirit and united to Christ and one another by faith. In Romans 12 we find the teaching often called theosis in Eastern Orthodoxy, where we are to 'offer our bodies a living sacrifice, holy, acceptable unto God...' and to do so as one body or group of believers. This is a grace given process of God working in us to make us more like Him.
Quote:
Romans 12:1–2: We are to present our bodies as a “living sacrifice,” doing so as part of our spiritual worship. And we are to “be transformed” by the renewing of our minds into the likeness of God.
1 Corinthians 3:16; 6:17: We are reminded that we are God’s “temple” and that “he who is joined to the Lord is one spirit with Him”—union with God.
Galatians 2:20: “It is no longer I who live, but Christ who lives in me.”
Philippians 1:21: “For me, to live is Christ.”
Colossians 3:3: We have “died” and our lives are “hidden with Christ in God”—total participation in Christ.
1 Thessalonians 5:23: May God “sanctify you completely”—complete conformity to the image and likeness of God.
2 Thessalonians 2:14: We were called by God “for the obtaining of the glory of our Lord Jesus Christ.”
1 John 4:17: “Because as He is, so are we in this world”—the possibility of deification, total participation in Christ this side of eternity.
John 17:22: In His high priestly prayer, Jesus says that He has given us the glory that the Father gave Him.
Revelation 21:7: At the beginning of the
eschaton, Christ says of each of us, “I will be his God and he shall be My son.”
1 John 3:2: “We know that when He is revealed, we shall be like Him, for we shall see Him as He is.”
Philippians 3:21: Christ will “transform our lowly body that it may be conformed to His glorious body.”
Source
The metaphysical foundation of the above is contained in the magnificent hymn of Colossians:
"... Who is the image of the invisible God,
the firstborn of every creature:
For in him were all things created in heaven and on earth,
visible and invisible, whether thrones, or dominations,
or principalities, or powers:
all things were created by him and in him.
And he is before all, and by him all things consist... "
(Colossians 1:15-17)
The passage cited above is explaining the preeminence of Jesus Christ who is, 'the image of the invisible God, the firstborn of all creation.' (v.15) If we continue on, we can see the theme of Christ being God and how we are now united with him in his death and resurrection resulting in salvation from sin.
18 And he is the head of the body, the church. He is the beginning, the firstborn from the dead, that in everything he might be preeminent. 19 For in him all the fullness of God was pleased to dwell, 20 and through him to reconcile to himself all things, whether on earth or in heaven, making peace by the blood of his cross. 21 And you, who once were alienated and hostile in mind, doing evil deeds, 22 he has now reconciled in his body of flesh by his death, in order to present you holy and blameless and above reproach before him, 23 if indeed you continue in the faith, stable and steadfast, not shifting from the hope of the gospel that you heard, which has been proclaimed in all creation[g] under heaven, and of which I, Paul, became a minister.
Paul continues to explain and then wraps up with,
2.6 Therefore, as you received Christ Jesus the Lord, so walk in him, 7 rooted and built up in him and established in the faith, just as you were taught, abounding in thanksgiving. 8 See to it that no one takes you captive by philosophy and empty deceit, according to human tradition, according to the elemental spirits[a] of the world, and not according to Christ.
Christians are rooted in Christ, tethered to him by the Spirit and we are to walk in unity with him and believers.
- Aetius