I'm going to be doing a series of posts on-and-off regarding ecumenism with the Orthodox.
The Orthodox, I think most people would now agree, represent a much more viable option for ecumenism than the Protestants. If we should have been trying to please anyone all these years, it was the Orthodox. Instead, we tried to Protestantize, and no one ended up liking us; the Orthodox are appalled by our current liturgical situation, for example.
Even though we are so much closer to the Orthodox, and there is such greater hope of reunion, once again, the Vatican's corrupt allegiance to "Western" culture won out back in the time of Vatican II, leading us to pursue in vain those heretics who happened to share a Western European history, rather than those strange Oriental folk with whom, nevertheless, we actually share the Faith itself. Yet it was a popular position for a time to think that we had more in common with Western Protestants (merely because they were Western) rather than with Eastern Orthodox (even though they are much more orthodox).
Of course, ecumenism continued on both fronts fortunately, and as of late the emphasis on the Protestant side has greatly decreased. They're finally realizing that we have no hope there except maybe for some traditional-minded Anglo-Catholics to jump ship, and we should really throw in all our cards with the East. And things seem to be progressing quite nicely there, especially with the Russians these days.
One great thing about the East is that I really do feel that it represents a sort of snapshot of the First Millennium Church. The problem, of course, is that the West has gone on to have doctrinal development and refinement since then, forming explicit crystallizations of ideas previously left more fuzzy...whereas the East sort of became frozen after the Seventh ecumenical council, believing anything not defined by then couldn't possibly be of the Faith since it wasn't already.
You can already find Orthodox who agree, essentially, with the Catholics on most issues, from the Immaculate Conception to Purgatory...but the problem is that they never officially "concretized" one formulation or another, so these all remain merely "theologoumenons" for them that admit debate and a variety of interpretations, and you will find other Orthodox who will vehemently reject such interpretations if only to deliberately distinguish themselves from Rome. And their authorities are reluctant to come down in favor of one interpretation for fear of alienating the other side, so there is a sort of ambiguity about certain teachings that the Western Church developed with more precision only in the Second Millenium.
For Catholics, it is hard to understand how the Orthodox can believe that development and refinement of formulation is possible for the Trinitarian and Christological questions (ala the first seven councils)...but then so much is left undefined and sort of vague for them about issues of ecclesiology, sacraments, grace and justification, etc. And yet, this was no doubt the situation in the First Millennium. Orthopraxy came long before any abstract formulations of the dogmas of the Faith. The Church was praying for the Dead long before it was ever explicitly spelled out exactly what state those dead were in and how and why our prayers for them are efficacious. It was recognizing Mary as All-Holy long before it ever explicitly discerned that this took the specific form of having Sanctifying Grace/Divine Life from the moment of her conception. It was believing in God, Father, Son, and Holy Spirit, long before terms like "substance" and "hypostasis" ever came into play, and was practicing the Eucharist long before the word "transubstantiation" was invented.
And yet such theological precision can be useful as long as it doesn't become too narrow or suffocating. As long as we don't turn the formulation of the dogma into the dogma itself, as long as we don't let the specific theological framework we parse the Truth in become confused with the Truth itself. It's true that such things like purgatory were rather fuzzy and not explicit before the 10th century or later. But, then again, things like the Trinity and Hypostatic Union were fuzzy before the 4th century. When looking at the Orthodox, I think Catholics can rightly ask why can there be clarification up to the 4th century or the 6th century, but then not for other questions up to the modern day?
I am convinced, personally, that there are no actual differences of Faith with the East, as much as strident voices on both sides might insist there are. But I have looked at all the doctrinal issues, and found them to be semantical. And, I think, there is a general recognition of this fact among the more nuanced heads on both sides (especially ours). The problems that remain are practical/political.
If the Orthodox could accept us wholesale today, I could accept them wholesale today. The Pope would, presumably, not dare interfere in any inter-Eastern or intra-Eastern affairs in the Church, and would only step in when there was a question with a disparity of jurisdictions both West and East involved; in other words, true ecclesiastical subsidiarity would be practiced. So they could continue in every way exactly the same as they do now, except we would be in communion, and they would let us receive communion their churches. But they wouldn't have to say anything different, they wouldn't have to do anything different...as long as they could accept the same tolerance for us.
There are some things, like the date of Easter and them putting the Pope's name in their liturgy...which it would be nice to resolve practically, of course, but that could come later. For example, I could see us agreeing to adopt the "Reformed Julian" calendar for our liturgy (it doesnt differ from the Gregorian for 600 more years, anyway)...if we could all agree to just calculate Easter based on the actual astronomy at Jerusalem instead of all the complicated tables. It would be better, as the New Calendarist churches in the East have messed up their whole liturgical year since the Sanctoral uses the new calendar, but Temporal doesnt, so certain overlaps can no longer occur (such as the Kyrio-Pascha, the coincidence of Annunciation and Easter) since the new calendar is 12 days back but the earliest and latest dates for Easter are not. But those things are disciplinary and non-essential. If we never reached an agreement about the date of Easter, we could still be one Church (some Eastern Catholic Churches still use Orthodox-style reckoning).
My point is, they wouldn't have to change any of their theological formulations, and wouldn't have to suddenly answer to the Pope in any practical questions as they seem to imagine. They wouldn't have to conform to the model that the Latin West currently uses vis a vis the Pope as Latin Patriarch (a role that, without an East to balance, has become somewhat confused and entangled with his role as Pope qua Pope). He wouldn't dare meddle in their internal affairs. They'd just exchange letters of communion each time a new Pope or Patriarch was elected. It would be otherwise totally the same, and hopefully would help act as a "counterbalance" to the power and centralizing influence of the Papacy in the West, and help reignite dynamic debate and dialogue in the Church, being mutually enriching.
However, while I believe the "dogmatic" issues are all entirely semantic, and that we actually teach the same thing (just we are "speaking Latin" and they are "speaking Greek" and something gets miscommunicated in translation), that our positions are complementary, not contradictory...still, I believe this must be made explicit. Statements must be made demonstrating how the two positions are the same and clarifying how they are complementary instead of contradictory, otherwise people will just be confused and both sides will look suddenly indifferentist or latitudinarian about doctrinal issues.
We can't, for example, suddenly say that the Filioque or Immaculate Conception are just Western theologumenons that may be safely ignored by the East. It must certainly be maintained that, given a Latin theological framework, as a Latin formulation, they are correct and dogmatic. But, at the same time, it must be admitted and demonstrated and agreed upon that the Greek formulations are also correct given a Greek theological framework, and are actually equivalent formulations of the same Truths, just with complementary emphases or perspectives. In other words, we're both right. We need to agree to that and demonstrate it convincingly.
If such reconciling explanations are not issued and agreed upon by both churches (perhaps in a third "neutral" language like English), I fear we lose clarity rather than gain it in a potential reunion. We give up the mutual enrichment by simply not addressing the issues, and thus make both sides look "wrong" instead of making both sides be right (which is the real solution).
Unfortunately, the current strategy seems to attempt to solve the semantical issues by having each side distance itself from its position. By making each side's position increasingly vague and blurry until they end up being so ambiguous that they would admit possible equivalency between them. This, I fear, is what happened with the Joint Declaration on Justification with the Lutherans. We didn't actually reconcile the two positions (impossible, because with the Protestants it isn't just a semantical "misunderstanding"...they actually believe something different). Rather, they simply phrased it in terms so broad and ambiguous that either side could fit their position under that umbrella. The same formulations were agreed on, but understood by each side as meaning totally different concepts.
What we need is the opposite. We need to allow a diversity of theological formulations with the East, while realizing that they actually are formulations of the same concepts, or we'll just end up with something as intellectually dishonest as the Joint Declaration again.
So, to that end, I'll be doing several posts soon, each on a certain concrete issue that allegedly divides us from the Orthodox, and attempt to show concretely and specifically how the two positions, in their separate formulations, are actually the same just with different emphases, complementary not contradictory. I'll try to point out where they're equivalent, and where each side might gain something through an encounter with the complementary emphasis of the other on that issue.