The reality of the Christian Church is one of division and disconnection. You have your Roman Catholics, your Eastern Orthodox, your Evangelical Protestants, your mainline Protestants, and a bazillion subdivisions in each of these. Yes, even the Roman Catholic church is a divided reality, they just have a great knack for keeping all the different fruits in one basket. (BTW I think baskets of fruit look purdy.) So this is the reality of the situation and there are a lot of folks passionate about bringing it all back together - if only so-and-so would change this little distinctive, uh well you get what I mean.
Unity (aka ecumenism) is an interesting problem for the Church. We love our distinctives. I for one am not willing to abide a patriarchal hierarchy such as our Roman kin enjoy. And I'm convinced that I shouldn't have to - both by my reading of scripture, my experience and my study of history. Flattening the distinctives of our movements into some sort of lowest common denominator or worse into a Darwinian loss of the weaker movements is not the way to unity. Unity is not something enforced but something embraced.
Unity begins with embracing that we all share a common starting point, despite our differences. One might be tempted to define this dogmatically, rooting it in a creedal formula, but I envision something a bit more unifying - history. We share a history - no matter where our movement took shape in this history, we all (as Christians) start with the experience of the primitive Church that told the stories of Jesus. That history belongs to every one of us who claim the name Christian - no matter what objections we have to what they've done with their heritage.
Unity continues to flourish when we begin to revel in diversity. If Social Trinitarianism has taught us anything it is that unity is only achievable in diversity (the other option is really totalitarianism). Diversity is helpful because it allows us to see the strengths and weaknesses of our own tradition/movements through the strengths and weaknesses of others. Iron sharpens iron is the proverb that comes to mind. Difference is the only thing that highlights our own uniqueness. Diversity is a prerequisite for robust life.
Unity results in strength. All that fundamentalism ever does is build polemics. It is a tiring defensive posture that has, frankly, eroded the public confidence in Christianity. It doesn't preserve, rather it stagnates. It can only end by turning in towards itself until it has no friends, a sad state I've witnessed over and over again. That is not strength, that is weakness.
Strength comes from knowing what and who you are. That we bring ourselves, unique and confident, into the diversity that is unity. That each of us makes up a part of the people of God, we identify with the Church as being our Church. This strength is the path of restoration of our place in the world as ones who speak for the poor, the lonely and the outcast. It is when the Church is united like this that we will once again be relevant to the world that God so loved.