One thought on ecumenism that I read somewhere and has stuck with me has to do with our preconceptions–or perhaps our frameworks.
The thought is: For well over a thousand years Christians thought of themselves as basically united–of the divisions among them over various issues as temporary and unfortunate. There was an expectation that eventually the divisions would be healed. Even in the centuries after the split of East and West–which we date to 1054–many Christians expected that unity would be restored in this unusual situation.
Only in recent centuries have we been formed to think of our divisions first–or of these divisions as primary for our identity. This has been a significant shift.
The ecumenical movement, it seems to me, will be succeeding when we think of ourselves first as united as Christians in Baptism–and work to heal the differences that exist.