Gradually, in time, I began to understand two key principles. First, Orthodoxy has no central body of "confessional documents" because it does not have a central hierarchical authority. This does not mean that Orthodoxy has no authority. It's authority is the authority of the Spirit of Christ, whose Word is enshrined in the Scriptures yet comes alive in the myriad chronological, historical and pastoral contexts of the Church.
Second, the closest thing that Orthodoxy has to a body of "confessional documents" is the liturgy. In Orthodoxy, the liturgy is inviolable because it is understood to be not of human origin but of the Spirit. (NB: "Liturgy" in Orthodoxy refers not exclusively or legalistically to the texts or rubrics.) Hence, as I once heard said, what is in the liturgy is what is to be believed. This puts the liturgy on par, then, with the various "confessional documents" common in post-reformational western churches.
On this latter point, the following words by the late Jaroslav Pelikan have proven quite helpful.
14.1 The Ambivalence of the Orthodox Church Toward "Symbolical Books"
Several factors in Christian history have often led to the issuance of confessions of faith, including the challenge from a hostile environment, the crisis of doctrinal schism, and the necessity of indigenization. A review of these would show that they have been at least as powerful within Eastern Christendom since the schism between East and West as they have been in the West, even in the West since the Reformation with its plethora of confessions. And yet, during most of the history of Eastern Orthodoxy, those factors did not produce a vast corpus of confessions of faith, as they had done in the early church and as they went on doing in the West especially during and since the Reformation, but only a select few statements of faith that became more or less official (and usually "less" rather than "more" official). As a result, to a degree that would not be true of most other communions that have official confessions, it is possible for two scholars almost exactly a century apart to speak about the "identity" of Orthodoxy without so much as mentioning these statements of faith. (399-400)
14.2 The Liturgy as the Church's Preeminent Confession of the Faith
A principal reason for this ambivalent position of "symbolical books" within Eastern Orthodoxy lies, however, in the distinctively Eastern versions, articulated in a special way in the Philokalia, of the inseparable connection between "the rule of prayer [lex orandi]" and "the rule of faith [lex credendi]." That connection has been important throughout Christian history, across the various boundaries of denomination and confession, also in the West. But interpreters of the Eastern Orthodox tradition, whether sympathetic or critical, are agreed on the proposition that within Eastern Orthodoxy The Divine Liturgy According to Saint John Chrysostom is an especially forceful illustration of the universal principle of lex orandi lex credendi; as noted earlier, it differs from the liturgies of other traditions, including even The Book of Common Prayer of Anglicanism, by being accorded a special position among the Eastern Orthodox confessions in the standard published collections of "symbolical books." Anastasios Kallis...introduced his edition of the liturgy with the explanation: "The identity of Orthodoxy consists neither in a doctrine nor in an organizational system, but in the correct praise of the Triune God, which has its center in the celebration of the Eucharist, or simply in the Liturgy, through which the one congregation assembled in the name of Christ becomes his body, his church." (405; emphasis added)
From Credo by Jaroslav Pelikan