Many years ago when I was at school (I left in 1972) I heard talk of something called the ecumenical movement whose aim was to bring all the churches together. For many reasons that hasn't happened not least because it seemed to be a top down attempt to force people into unity.
A few years ago I was the Churches Together in Beckenham treasurer and while we did manage to work together this was done by agreeing on a small set of common beliefs (the Apostles Creed) and ignoring our differences. We used to joke that it was easier to get the Baptist, Roman Catholic, Methodist and United Reformed churches to work together than it was to get all the different Anglican churches to stay in the same room. Progress was made in that we found we could work together and the idea that you were in a denomination for life was weakened, even if it is still with us.
The problem I see now is that we have formed cross denominational groups which share a common theology and getting these groups to work together, or even accept each other, is possibly harder than working across the denominational divides. At it's simplest this means liberal and evangelical groupings (but I suspect it could be broken down a lot further) and some of these groupings don't accept that the others are really Christians and others look down on the rest as intellectually inferior.
The ecumenical challenge we face is the task of accepting each other exactly as we are instead of looking for a small set of common beliefs. For example this means biblical literalists have to accept that Christians who do not share their belief are not 'bad Christians' and those Christians in turn must accept that the biblical literalists aren't intellectual idiots. I am under no illusion that this will be easy but I do know where to start, I have to start with me. If all Christians start to treat each other with love and respect just think what a difference that would make.