ἵνα ὦσιν [present active subjunctive 3rd person plural] ἓν καθὼς ἡμεῖς
(John 17:11, ESV) -- "that they may be one just as we are [one]."
The hint as to how we are one relates to how people will recognize us as Christ's disciples.
A new commandment I give to you, that you love one another: just as I have loved you, you also are to love one another. 35 By this all people will know that you are my disciples, if you have love for one another.”
(John 13:34–35, ESV)
At the last supper Jesus began showing his love.
Now before the Feast of the Passover, when Jesus knew that his hour had come to depart out of this world to the Father, having loved his own who were in the world, he loved them to the end. (John 13:1, ESV)
It started with washing his disciples feet.
Do you understand what I have done to you? 13 You call me Teacher and Lord, and you are right, for so I am. 14 If I then, your Lord and Teacher, have washed your feet, you also ought to wash one another’s feet. 15 For I have given you an example, that you also should do just as I have done to you.
(John 13:12–15, ESV)
And, Jesus' ultimate display of his love was dying for us.
This is my commandment, that you love one another as I have loved you. 13 Greater love has no one than this, that someone lay down his life for his friends.
(John 15:12–13, ESV)
Jesus said his kingdom is not of this world.
My kingdom is not of this world. If my kingdom were of this world, my servants would have been fighting, that I might not be delivered over to the Jews. But my kingdom is not from the world.”
(John 18:36, ESV)
He also said we must worship in spirit and truth.
But the hour is coming, and is now here, when the true worshipers will worship the Father in spirit and truth, for the Father is seeking such people to worship him. 24 God is spirit, and those who worship him must worship in spirit and truth.”
(John 4:23–24, ESV)
Then Pilate said to him, “So you are a king?” Jesus answered, “You say that I am a king. For this purpose I was born and for this purpose I have come into the world—to bear witness to the truth. Everyone who is of the truth listens to my voice.” 38 Pilate said to him, “What is truth?”
(John 18:37–38, ESV)
If God has revealed Himself in absolute truth to Christians, why do Christians have so many denominations with different viewpoints? God clearly defined the physical form of worship in the Old Testament (a clear description of the tabernacle and priesthood), but that external form didn’t reach the inner person. The New Testament describes what a church member (the individual) should be, but does not give a clear picture of the structure of the church leadership. The New Testament message emphasizes an internal conversion through Jesus Christ’s sacrificial death and the Holy Spirit’s residing.
Can we say that God has a purpose for the many Christian denominations today? Given the nature of humanity, a better question is: "If Christianity were a single denomination, would that really accomplish God’s intended purpose of reaching people from the inside out?"
Ephesians 5:1 – 6:9 is an example of how Christians should be one with God.