This is more true, and much more important than many realize.
I pray not only for them, but also for those who will believe in me through their word, so that they may all be one, as you, Father, are in me and I in you, that they also may be in us, that the world may believe that you sent me. And I have given them the glory you gave me, so that they may be one, as we are one, I in them and you in me, that they may be brought to perfection as one, that the world may know that you sent me, and that you loved them. (John 17:20-23)
Our unity is one of the ways in which the world knows that Jesus is who we claim him to be. Without unity, the world will not know that Jesus Christ is the Second Person of the Trinity sent by God the Father. Without unity, Jesus is just another man in some ancient book.
Our unity is how the world knows, proof that God loves us!
And for us personally, we are brought to perfection “As one.” One of the ways in which we attain perfection, and hence the ability to enter Heaven, is through our unity as a group, as a single body which is the Body of Christ. Christ had one body, and it is through that body - the Church - that we attain perfection.
With the exception of the agony in the garden and his cries from the cross, Jesus’ prayer for unity is perhaps one of the most passionate and heartfelt of all his prayers and is one of the most dramatic moments in all of Scripture (IMO). I think Jesus prays for unity with good reason. I order to witness to the world and to attain to perfection, we need to maintain unity to the extent that we are able, even if it means putting aside our own will to do the will of another, or simply biting our tongue.
Ours is the only religion where our faith, prayers, good works and suffering can merit the salvation of someone else and we are all in this together. St. Paul understood this clearly and our disunity, not just within east/west relations but within our own rites is worse than many of us realize.
-Tim-