Hello Justin
It isn't necessary for me to read what Archbishop Rowan Williams had to say to a group of Muslims to know what Orthodox Christianity is. Orthodox Christianity is not a response or reaction ot Islam, except in one instance.
Modern Christians have a difficult time wrapping their minds around what early Christianity was actually like. They seem to think early Christians were much like today. That we could find Bible thumping evangelicals and fundies in the early church, that the modern church is pretty much simply a continuation of what existed in the past. Such is not the case.
Orthodox Christianity, in its simplest most authentic expression, resulted as a reaction to the teachings of various "heretical" movements/teachings. People weren't running around with their personal copies of the Bible. There were no Bibles. It would be hundreds of years before the canon of Scripture was settled upon, and over athousand years before the invention of the printing press began to make printed copies of the Bible affordable for everyday people.
Instead, the early church had a certain oral tradition, a "catholic" (small c) tradition, of the content of the Christian faith. It existed separate from the NT, which did not yet exist as an authoritative body of fixed books which could be consulted. The faith was expressed mainly in the annual Liturgical cycle of feasts and fasts, in iconography, hymnody, the sacraments. A sort of Christianity via consensus of participation, not simply a Christianity via an abstract intellectual conception of theoretical dogmas. The early church lived it's faith, it did not sit around studying it faith from a nonexistent unavailable Bible. This is so hard to get fundiots and their somewhat brighter cousins, the evangelicals to understand.
For the early Church, Christianity was not a list of abstract dogmas to be believed but a way of life in union with Christ that was to be expressed within the community of faith via participation not via ratiocination as it is in modern Thumper religion. Christianity was a complex and rich fabric not of abstractions but of culture. Music, art, processions, chants, prayers, psalms and hymns, of an entire yearly cycle of various commemorations that were not simply dead holidays as they are today. It was a total immersion into a living faith Tradition lived out in community that predated the Bible.
When various "Heretics" arose, they were recognized as such not because someone had a NT and was able to quote Book, Chapter, and Verse (in fact, it was the heretics that first resorted to this method as they do today), but were recognized as heretics because their teachings and practices were not part of the Tradition, a Tradition that incorporated every aspect of life both communal and individual. Christianity was personal, but not private as it is today. It was very much a communal life. By communal I mean community. Today Christianity among protestants, evangelicals, and fundys is not only personal but private. "Me and Jesus and my Bible." Such a life completely denies the nature of the BODY of Christ and in fact encourages and expects each part of the Body to be off doing its own thing.
So, when one of the earliest arch-heretics arose, Arius, his novel teaching caused great commotion among the community of faith for the simple fact they were not the majority consenus. Arius appealed to the Bible, as do the 35,000 sects today, rather than the Tradition. He nearly succeeded in changing Christianity from a faith that lived the Deity and true humanity of Christ to one that denied it. Athanasius was the hero of the day, having penned a brilliant refutation of Arius titled On The Incarnation which is available in English. It was on the basis of the Tradition, the Consensus, that was lived out by each memeber of the Body of Christ, that heretics such as Athanasius were defeated.
This process continued for many centuries. As new heretics and heresies arose, the Tradition of faith was the final arbiter, over and against the Bible-wielding heretics. The church fell back upon Christianity as they had lived it and known it for centuries. In reaction to these heretics the church formulated and adopted a number of doctrinal positions that were expressed in creedal form. For the Easter or Byzantine church, this process came to a close with the Second Council of Nicea in the ninth century I believe. The Byzantine church recognizes a total of seven such councils, which are referred to as Ecumenical because most of the various geographical expressions of the church catholic participated and later ratified these councils. The Western, or Roman half of the church catholic continued these councils for many centuries more. However, since such Roman councils were not truly Ecumenical (did not include the many Eastern churches and Patriarchates).
So, my answer to you is an historical one. Orthodoxy is that type of Christianity that does not simply have the Bible as its base (which results in the unstoppable sectarian splintering that has become a cancer on the life of the church since the Reformation), but the continuous living Tradition which it had known and lived from the beginning.
Any other answer is a purely subjective one, based on the answerers own personal/private interpretations, or their own narrow (and recent) sects abstract understanding of Christianity.
Nathaniel J. Merritt
December fifth, 2005