Ecclesiology is the theology of the Orthodox Christian faith concerning the Church.
The Church is the Body of Christ, a theanthropic (divine-human) communion of Jesus Christ with his people. The sole head of the Church is Christ. The Church is an object of faith, that is, Orthodox Christians believe in the Church. The traditional belief in the Church is attested to in the Nicene-Constantinopolitan Creed as the one, holy, catholic and apostolic Church. By this phrase is meant that the Church is undivided and not many (one), sanctified and set apart for the work of God (holy), whole and characterized by fullness and universality (catholic), and has at its essence the going out into all the world to preach the Gospel and baptize the nations (apostolic).
The Church is the Bride of Christ, the eschatological spouse of the Son of God, united to him in faith and love, for which he gave himself up on the cross. The intimacy of a husband and wife is an earthly image of the intimacy that Christ has with his Church, and the union of an earthly marriage is a shadow of the union of that marriage of the Lamb of God with the Church.
The community of the Church is the locus of salvation for mankind; it is truly the Ark in which mankind may be saved from the flood of corruption and sin. In it, Christians sacramentally work out their salvation with fear and trembling (Phil. 2:12), worshipping the Holy Trinity in spirit and in truth. The Church is the pillar and ground of truth (I Tim. 3:15) and thus may be relied upon in the Christian's struggle to apprehend the one truth for himself. The Church is eternal, and the gates of Hell will never prevail against it (Matt. 16:18).
The Church consists of the prophets and saints of both the Old and New Covenants, the angels and the concrete, historical community of believers in this earthly life. Those who have gone on before us are known as the Church Triumphant, while those in this life are known as the Church Militant.
The boundaries of the Church are ultimately known only to God himself, but outside the historical context of the Church—that is, the Orthodox Church—the nature of the connection of any human being to the Church (whether a believer in Christ or not) is unknown to us. Throughout Church History, various groups have broken from the Church, a tragic reality which does not divide the Church but rather divides believers from the Church. The final status of Christians in such communities is dependent on God's mercy and grace, as is the case with those with membership in the Church in this life.
- The Orthodox Understanding of Primacy and Catholicity, by Bishop Hilarion of Vienna and Austria (paper read at the meeting of the theological commission of the Swiss Bishops' Conference in Basel, 24 January 2005)