The Orthodox Church simply calls herself "the Church," just as the Greeks in the past used the word "Christians" to refer to the Orthodox. This follows naturally from the fact that the Eastern Orthodox Church is organically the same congregation or ecclesia which was born at the outpouring of the Holy Spirit in Jerusalem on Pentecost. In many places already mentioned in the New Testament this congregation has remained the same throughout history. The Orthodox Church does not need to give proof of her historical authenticity; she is simply the direct continuation of the Church of the Apostolic Age.
Does the Orthodox Church of today in fact correspond to the picture we get of the congregation of the Apostolic Age when we read the New Testament and the writings of the Apostolic Fathers? It does -as much as a grown-up person corresponds to a picture taken of him as a child. Although the Church has developed, it is the same in essence and spirit in the twentieth century as it has been from the beginning.
The coming of Christ when the time was "fulfilled" (Mk 1: 15) was an appointed event; indeed, our calendar begins there. The outpouring of the Holy Spirit in fulfilment of the "promise of the Father" (Arts 1:4) was also an appointed, unique historical event. For the Church it meant power from on high" and "the Spirit of truth" (Lk 24:49, Jn 16:13). On the strength of this we believe that although the grace of the Holy Spirit is at work in the later churches and communities according to their faith, the plenitude Of grace once given to the Church in the historical outpouring of the Holy Spirit will not be given again. In a hymn for Pentecost the Church sings:
Blessed art Thou, O Christ our God, who hast revealed the fishermen as most wise by sending down upon them the Holy Spirit; through them Thou didst draw the world into Thy net. O Lover of man, glory to Thee!
"When the Spirit of truth comes He will guide you into all the truth," Christ promised (Jn 16:13). After this promise had been fulfilled, the Apostle indeed gave to the "Church of the living God" the name "pillar and bulwark of the truth" (1 Tim 3:15).
The promised gift of "all the truth" came to the Church in the outpouring of the Holy Spirit, but it took centuries, the whole Patristic Age, to define it using man's limited concepts. And although the Fathers were learned men, profound thinkers, and pure in their lives, this alone is not enough to guarantee the absolute character of the truth inherited from the time of the Fathers. Therefore we need the power of the Holy Spirit, which was given to the Church, to guide it to the truth and to protect it. The verbal formulations of the faith which was in the consciousness of the Church from the very beginning have developed over a long period. Similarly, the whole ecclesiastical life has found richer and richer expressions in the various parts of Christ's Church which differ from one another in form but not in spirit. Thus every attempt to create an apostolic congregation, disregarding the work of the Holy Spirit which has gone on in the Church for two thousand years, seems artificial from the Church's point of view.
Just as Christ has both a divine and a human nature, so has the Church. On its human side the Church is susceptible to errors, weaknesses and failings, but it has consolation in the promise: "I will build my church, and the gates of hell shall not prevail against it" (Mt 16:18). This means that though the storms of time may ravage the human substance of the Church, they will not destroy the Church. The Church will endure until the next period of God's rule over the world is ushered in, until the parousia or Second Coming of Christ. Until then the church which was established at the first Christian Pentecost will endure as the protector of the truth, maintaining its characteristic features of apostolic priesthood, the Eucharist and other sacraments, and the common experience of the Church, its Tradition.