Byzantium can in no way be considered merely a completed and outlived chapter of Church history. Not only does it continue to live in the Orthodox Church, but in a sense still defines Orthodoxy itself, constituting its historical form.
Just as modern Catholicism crystallized in the Middle Ages and in the era of the Counter-Reformation, so — perhaps to an even greater extent — did Orthodoxy acquire its present form, its historic canon, in Byzantium.
Simple inquiry will soon show that any aspect of modern Orthodox Church life to which one might refer found its present-day form in the Byzantine period in particular.
The development of the Rule of worship was completed in Byzantium, a Rule, which makes of it a system permitting almost no progress or change.
The Byzantine typicons and euchologia of the thirteenth and fourteenth centuries differ hardly at all from our own missals and rule-books.
The Orthodox icon is painted in accordance with the Byzantine tradition; our canonical tradition was fixed in both volume and interpretation by Byzantine canonists.
The patristic heritage, which has until now been the basis of Orthodox theology, was given final shape in Byzantium, and there first flowered the manner and spirit of Orthodox piety which is best expressed in Russian by the word tserkovnost.
In a sense the Byzantine period must be acknowledged as decisive in the history of Orthodoxy, as the age of the crystallization of Church life.
The modern Orthodox Church is — from the viewpoint of history — the Church of Byzantium, which has survived the Byzantine Empire by five hundred years.