Jesus wasn't in the habit of making new commandments. He was actually mostly interested in reviving old ones. But Jesus' one new commandment was simply for his followers to love each other. That's simple, right? And yet it has evaded us throughout church history.
Jesus asked us to love each other. This love was, in and of itself, the fabric of all the other things Jesus set out to do. It was the essential fabric of Jesus' laying down his life on our behalf (no matter how you choose to work that out theologically). Love wasn't to be a strategy for changing the world, but it would, on its own and by its own virtue, be the fabric of the world's healing.
What did we do with this command? We turned it into a method for accomplishing other things. We missed love and chose instead to focus on all the stuff that was meant to point us toward love. We got really excited about theology, but forgot to do it for love's sake. We got really excited about evangelism (or sometimes just flat-out imperialism), we tried to make everybody into church-people and forgot to share the really good news. Sometimes we even got excited about liberating oppressed people or bringing economic revolution, but we forgot that love was the only true substance of action. We even got excited about love itself sometimes, but only because we thought it would make us better at a host of other things. We forgot to love for love's sake. We built a shrine to the things which were themselves supposed to be shrines to love.
The fact, in light of the gospel, is that God is love. So until we learn to love for love's sake... until we learn that being in relationship is not a means to an end or a strategy for evangelism... until we learn that love has nothing to do with accomplishment, we'll never be able to accomplish the things of that only love can accomplish (that's a paradox, I guess). Until the church is a place where humans can love one another for love's sake, it will always be a church of something other than Christ.... and paradoxically, because of love, we are Christ's church even in our failure to be so.