“We” are all members of the Body of Christ to the extent that we are in communion with the Body of Christ, the Church

And does not baptism bring about that communion, at least to some degree? As a Catholic I am connected through the sacraments with Christ, and through Christ with my fellow Christians, regardless of ecclesial status. Is this not a reasonable manner in which to speak of communion? Grace flows to all from the same source.

ROCOR has had a very closed communion has gone so far as to deny the efficacy of Sacraments of other Orthodox Churches IIRC, and I think part of the understanding may stem from there. There are other and deeper seeming contradictions out there. For example, the Jewish race is the chosen people, but then we are told the Lord was with the Gentiles the entire time and there are gentiles in fact with the Lord.

Is this just historical accuracy or is there some kind of diplomatic overture going on here?

On the Orthodox side there are more serious beefs, and rightly so. I sense more willingness on the Catholic side to smooth over differences, as evidenced by Eastern Catholic churches’ full communion with Rome. But they’re not going to give up their insistence that the pope of Rome by recognized as head of the Communion of Catholic Churches by any church wishing to gain full communion. The Orthodox have no such desire, of course.

The “imperfect communion” is the Catholic way of saying, “close enough.” From the Orthodox perspective we’re is a state of non-communion, but on the Catholic side the “close enough” allows him to come to my church and receive the Eucharist. My priest would have no impediment serving him the Eucharist (his priest would not take the same view, if I understand correctly). And since the celebration of this sacrament is, in the Catholic understanding, what constitutes a church, and the fact that we can share this sacrament means we’re in communion, though imperfectly.

I know that leaves much to be explained. The “imperfect communion” seems to me to weaken the Catholic insistence on the primacy of the pope of Rome over the Communion of Churches. And if anyone can explain to me that this is not the sticking point (for Rome), please do so.

In Catholic teaching, 3 conditions need to be met for a mortal sin (such as schism) to be committed. (Here is an explanation of the 3 conditions, the first link I found when I googled, but it looks adequate.) If any of those conditions are absent, then a sin is not committed, i.e. there is no true schism, although what we do and say may seem like schism. If I am in the state of grace, united with God, and do what I believe to be in accordance with His will (and I am not culpably ignorant of what He wants), then I remain united with Him, even though I do not do all that is in accordance with His will (like be in communion with the Bishop of Rome, as Pope), because of my ignorance.

Likewise, it is not really a compliment to say that such-and-such a religion has some of the truth, since the fullness of the truth is the only thing efficacious for salvation. I suppose the point would be that if non-Catholics can have valid orders and sacraments, and thus have hope of salvation in the confessions in which they currently are, there is no real reason to ever leave those confessions. While this is a very diplomatic thing to say, I don’t quite understand how you finally square it with the claim that the fullness of truth is in the Catholic Church alone.

Perhaps the more difficult thing is how it is possible for Catholics to speak of the Orthodox as being true Churches?