Any list of the defining moments of Christian history -- if not the history of religion on Planet Earth, period -- would have to include the Great Schism of 1054.
That's the split, of course, between the Orthodox East and the Catholic West and there is hardly anything that you can say about the who, what, when, where, why and how of that schism that will not lead to a millennium or two of debate. It's complicated.
However, it's pretty easy to understand that the Church of Rome and the churches of Eastern Orthodoxy are not in full Communion -- with a big "C" -- with one another. The primary symbol, and reality, that demonstrates this is that their clergy cannot celebrate the Eucharist together.
Now, with that prologue, let's flash back to the recent meetings in Istanbul between Pope Francis and the Orthodox Ecumenical Patriarch Bartholomew. Since I am Orthodox, lots of people have asked me what I thought about their latest statements on their desire for full unity, meaning Communion. My question, in response, was: Yes, the pope asked Bartholomew to bless him, but did either man kiss the other man's hand? There was also quite a bit of confusion about the rite they took part in at the Phanar.