Given that in John 17 we get to listen in to Jesus High Priestly prayer for us concerning our Unity, it is interesting to me that we don't see this highlighted more in sermons, books, and prayers. The promise is clear: "May they be brought to complete unity to let the world know that you sent me and have loved them even as you have loved me", and the implication in the next few verses is that this desired unity points directly to God's Glory. That being the case, it is totally worth striving for, considering the enormity of what is at stake in our worship and in witness.
This was beautifully illustrated for 10 of us recently in the Bill Drake Band Tour of Germany, May 2010. For 19 days we toured Germany, Austria, and Switzerland. We diligently protected our unity in prayer, worship, devotion, and attitude to such an extent, that in all honestly, not once during the entire tour did any of us have a single argument, harsh word, or terse disagreement. The results were physically tangible.