John 17 is known as "The High Priestly Prayer." Jesus prays before being arrested, and his prayer is on our behalf (hence "priestly" -- going to God for the sake of others). We're used to thinking about Jesus wanting us to be saved and to live holy lives, but the High Priestly Prayer gives us another emphasis from Christ: Christian unity.
This is what Jesus prays in John 17:20-23: "My prayer is not for them [the Twelve] alone. I pray also for those who will believe in me through their message, that all of them may be one, Father, just as You are in me and I am in You. May they also be in Us so that the world may believe that You have sent me. I have given them the glory that You gave me, that they may be one as We are one -- I in them and You in me -- so that they may be brought to complete unity. Then the world will know that You sent me and have loved them even as You have loved me."
In a world of thousands of Christian denominations, it would seem as though this prayer went unanswered. Christians have split and fractured almost since the Church began. Initially these schisms were treated very seriously; some early Church Fathers thought it was worse to cause a split than to reject the gospel outright. Nowadays, we tend to split churches and start new denominations at the slightest provocation, with everything from taste in music to the color of the carpet being a valid reason to begin a new church.
It shouldn't be this way. We should all band together under the banner of Jesus Christ, preaching the same gospel and showing the same love of the same God to the people. We need to work together for the sake of the lost. After all, the name of your denomination can't save you. The paint scheme of the sanctuary can't atone for your sin. The only one who can save and whose blood made atonement is Jesus Christ, and he's the one who unites us all in his salvation.