Reunion: Is it possible?

So far as I can judge from reviews and from the numerous letters written to me, the book [Mere Christianity], however faulty in other respects, did at least succeed in presenting an agreed, or common, or central, or 'mere' Christianity.... If I have not directly helped the cause of reunion, I have perhaps made it clear why we ought to be reunited.
C.S. Lewis, Mere Christianity (1952; Harper Collins 2001) xi