They may be one even as we are one

On the night before the arrest, Jesus prayed with his disciples in John 17:

20 “I do not ask for these [disciples in the room] only, but also for those who will believe in me through their word,

i.e., future believers like us

21 that they may all be one, just as you, Father, are in me, and I in you, that they also may be in us,

Spiritually speaking, that is accomplished through the Paraclete indwelling spirit.

so that the world may believe that you have sent me. 22The glory that you have given me I have given to them, that they may be one even as we are one, 23I in them and you in me, that they may become perfectly one, so that the world may know that you sent me and loved them even as you loved me.

Earlier in same evening in John 13:

34A new commandment I give to you, that you love one another: just as I have loved you, you also are to love one another. 35By this all people will know that you are my disciples, if you have love for one another.”

Practically speaking, Christians loving one another will prove unity in Christ to the world/people.

Vertically, the Paraclete in every Christian's spirit connects every one of us to God to form a spiritual Body of Christ. This oneness is an undeniable perfect spiritual reality.

Horizontally, how do non-believers observe this oneness physically? They can see the fruit of this oneness in Paraclete if we love one another in Christ. Unfortunately, many Christians are not practicing this new commandment of loving one another, due to selfishness, doctrinal divisions, etc.

Jesus prayed for this showing of oneness in all his followers. It must have been important to him. For my part, I'd try to be less selfish, more objective, humble, meek, and loving toward my brothers and sisters. Also, to avoid bickering on doctrinal isms, I employ a denomination-free, disciplined logical approach to Biblical interpretation.