Of course the elephant in the room is the glib Roman presumption that unity will take place under Papal authority, rather than the Roman Church coming back into the Byzantine fold, with the Patriarch of Rome abandoning his claims of universal primacy and personal infallibility.
That, and whenever reunion is talked about by Romans, it is always assumed that there are no serious theological differences remaining, just a few quibbles over terminology.
Nothing could be further from the reality.
The filioque remains a huge issue, cutting to the very heart of Orthodox theology. It is not a question of whether “and the Son” was inserted canonically or not, or even if the Eastern version (that is, the *original *version) can be recited, with the Roman addition unspoken but understood. The idea of the Holy Spirit co-proceeding from the Son not only compromises the Father as the unique “source” of the other Two, but necessarily a mutual begetting of the Son as well, and with the Persons of the Holy Trinity defined thus by their relationship to each other, you approach the old heresy of Modalism. It is not a phrase to drop in or out at will!
The question of original sin is also more than simple semantics, and again, the issue cuts deep into Roman doctrine, most specifically with regard to the so-called Immaculate Conception – I’ll not go deeper into that here. Also the Roman definition of Transubstantiation – Orthodoxy is content to leave the miracle of the Holy Eucharist a mystery, and rejects the blueprinting of God’s work. Additionally, many skeptics make valid objections to transubstantiation – if the “essence” is fully changed, and only the “accidents” remain, why must those with wheat allergies avoid the Host? And why does the Blood still intoxicate if the alcohol is not there? These are great and holy mysteries which the popes claimed to lay out like a math equation.
Only when Rome abandons her unlawful and wild speculations and innovations will the Holy Church again be one, inshallah.
