Roman Catholics and undiscerning Protestants miss the point of Jesus’ prayer for unity in John 17. They think that this unity is to be found in a denomination.
This unity for which Jesus prayed takes place when believers are baptized into Christ. The fullest expression of this unity is love. Just as the Father is in the Son, Jesus prayed that the church might too “be in us” so that “the world may believe” that Christ was sent by the Father. The world cannot see the reality of believers "being in us", but it can witness love. So, Jesus is very clear that the witness to the world is love and the source of that witness is union with Christ and in him union with the Holy Trinity: “I in them and you in me – so that they may be brought to complete unity.” Jesus went on to pray: “Then the world will know that you sent me and have loved them even as you have loved me." Finally, Jesus closed his prayer with these words: "I have made you[ known to them, and will continue to make you known in order that the love you have for me may be in them and that I myself may be in them.”
There we have it. Through union with Christ the love of the Father for the Son may be in those in Christ, just as Christ himself indwells the believer. Yet m
any Roman Catholics, like Bryan Cross, think that unity entails all believers falling under one “Bishop” at Rome. But quite the contrary is the case. After all, Jesus prayed that his people might be kept from the evil one.
Only love is sufficient to demonstrate the harmonious nature of true unity. Yet, as we are well aware this side of glory, being part of the same denomination is not sufficient to display love, let alone unity.