By loyalty we are united to Jesus Christ, He is our Unity.
The basis for unity of all who are spiritually congregated around Jesus is Jesus himself. When Paul writes to Timothy (1Tim.3:15) and describes “the congregation of the living God” as the pillar and support of the truth, He is continuing to think of those truly united to God…the remnant of Israel, as opposed to the larger, but disloyal, body of people called Israel, who nonetheless still congregated periodically at the temple in Jerusalem. There is a unity which I ought to charitably assume belongs to those individuals marked by loyal acknowledgment of Jesus (not circumcision). It is those who are marked by loyalty, or loyal acknowledgment, to Jesus who are spiritually congregated around Jesus. Their unity is expressed locally when disciples gather together on the basis of nothing more, and nothing less, than shared loyalty to Jesus. Loyalty to Jesus, with Him as our distinct, and singular point of unity, requires a supernatural focus and I think that is why Jesus was praying we would have this unity in John 17.