[Please note: The following are personal musings and not to be construed as *the* Orthodox understanding. If anything here contradicts the received teaching and way of life of the (Orthodox) Church, please correct me. As always: check with your priest or spiritual father.]
Because the meanings of “Christianity” are diverse, the description of what is meant by “Christian ecumenism” can take any of several directions.
On the one hand, ecumenism is “interfaith dialogue” between representatives of diverse faiths, not necessarily with the intention of reconciling the professors of other faiths into full, organic unity with one another but simply to promote better relations. With some Christian perspectives on ecumenism, there is no other principle of ecumenism than this. They aim only toward the promotion of toleration, mutual respect and cooperation, whether between Christian churches and denominations, or between Christianity and other faiths. Thus, the World Council of Churches is an instrument in both, the Ecumenical Movement and the Interfaith Movement. However, this is not the case for all Christian ecumenical initiatives; and it would be difficult if not impossible to discuss them together, when much of the Christian world makes a definite difference between the two ideas. Therefore, readers are referred to the thorough discussion of ecumenism in the sense of the promotion of mutual appreciation and improvement between diverse religions, under the entry on religious pluralism.
On the other hand, ecumenism means the aim to reconcile all who profess Christian faith, into a single, visible organization, for example, through union with the Roman Catholic Church, or the Orthodox Church. Ecumenism in this sense focuses on the special problem of the relationship between Christian denominations, where Christianity is dogmatically defined.
This distinction between the two primary understandings of ecumenism (Protestant and Orthodox/Roman Catholic) is extremely important. Protestants find the Orthodox insistence on being the one, true, visible Church tiresome. But that is because Protestants come at the issue of ecumenism from a completely different ecclesiology from Orthodoxy.
Although I readily concede the following to be somewhat superficial, generally, I think it correct to describe Roman Catholic ecclesiology as “one over many” where unity obtains (in part) administratively in the see of Rome; Protestant ecclesiology as “many over one” where unity obtains pluralistically; and Orthodox ecclesiology as “both one and many” where unity is the catholicity of the local Church at the same time that it is the plurality of all the local Churches. With regard to Protestant ecclesiology, then, from the Orthodox perspective, the error is a mirror image of the Roman Catholic error. Whereas the Pope is the locus of the instantiation of the infallibility of the Church, in Protestantism, infallibility is instantiated in the individual. Whereas the Roman Catholic Church’s unity is a visible adminstration linked to Rome, in Protestantism, the unity is necessarily invisible, and secured through the individual’s adherence to his interpretation (and as many people of like mind with whom he can associate) of what constitutes the apostle’s teaching. Whereas the Roman Catholic Church’s apostolicity is historically tangible in episcopal succession and fidelity to conciliar dogma, in Protestantism, apostolicity is necessarily and exclusively doctrinal. So, for Orthodox, the Protestant ecclesiological error is bound up with that of the Catholic.
For Orthodox, Church unity is visible, incarnational, historical. For Protestants, Church unity is invisible, spiritual, and ahistorical. Protestant church unity is based on doctrinal agreement and the willingness to endure contradiction. That is to say, one will find the common denominator to which all can say “Amen,” and allow the differences, however substantive, to not matter. (One can see how easily portable this methodology is from the context of intra-Protestant dialogues to that between different faiths entirely.) But is this even Christian? (Cf. 1 Timothy 3:15)
Note here the substance of my complaint: It is not that Protestants aren’t Orthodox. It’s that Protestants have an ecclesiology that cannot be reconciled to Orthodox ecclesiology, and therefore ecumenical efforts cannot be aimed first at union. If two parties cannot even agree on what the endpoint should be, in what way can their efforts be fruitful? That is to say, for Orthodox, ecclesiology is not merely a doctrinal point, but a way of living. And one can only assume this is true of Protestants as well. This being the case, then, until Protestants change their ecclesiology, there can be no union. (More on that point later.) Protestants may be satisfied with toleration, respect and an invisible “unity.” But Orthodox cannot be so satisfied.
[This is a first in a handful of reflections I want to make on the matter of Church unity.]