The church is a microcosm of the Holy Trinity and cannot be divided into branches which are at odds, lest the Holy Trinity be considered schizophrenic. St. Maximus the Confessor tells us that:"An Icon of the Triadic God is the Holy Church, as she operates the very union among the faithful to God, albeit to those who happen to be of different speech and from different places and customs, according to which [union], by the faith, are made one." (Patrologia Graeca, vol. 91 “Mystagogy,” ch. i, p. 668 B)
St. Photius the Great further states: "Wherefore, on the one hand, the unity of the Trinity towards itself, it is lawful to say, FORMED A CHURCH [Greek: ἐκκλησιάσασα, i.e. “was congregated”], while on the other hand, it is lawful to say, that, at the moment of the creation of mankind, the term “let us make man in our image and after our likeness,” was bestowed upon created man in oneness of opinion, and thereby the creation of mankind from shattered creation was prepared..." (Homily 9:9)
Pertaining to the Church, Saint Theophan the Recluse wrote the following: “What is the holy Church? It is a society of believers, united among themselves by a unity of confession of divinely revealed truths, by a unity of sanctification by divinely established Mysteries, and by a unity of government and guidance by God-given shepherds. The oneness of confession, sanctification, and administration constitutes the rule of this society, which is obligatory for anyone who joins it. Membership in this society is contingent upon accepting this rule and agreeing with it; remaining in this society is contingent upon fulfilling it. Let us see how the holy Church grew and how it continues to grow. The preachers preach. Some of the listeners do not accept the preaching and leave; others accept it and as a result of accepting it are sanctified by the holy Mysteries, follow the guidance of the shepherds, and thus are incorporated into the holy Church -- they are churched. That is how all the Church‘s members enter her. In entering her, they are mingled with all her members, they are united with them, and they remain in the Church only as long as they continue to be one with them all.”
St. John Chrysostom tells us, “Nothing is more abiding than the Church: she is your salvation; she is your refuge. She is more lofty than the heavens; she is more far-reaching than the earth. She never grows old; she always stays in bloom. And so Scripture indicates her permanence and stability by calling her a virgin; her magnificence by calling her a queen; her closeness to God by calling her a daughter; her barrenness turned to fecundity by calling her 'the mother of seven'. A thousand names try to spell out her nobility. Just as the Lord is called by many names - Father, Way, Life, Light, Arm, Propitiation, Foundation, Gate, Sinless One, Treasure, Lord, God, Son, Only-Begotten, Form of God, Image of God, - since one name could not hope to describe the Omnipotent, and many names give us some small insight into His nature, so the Church goes by many names.”
The Council of Bishops of the Russian Orthodox Church Outside Russia, 1983, signed by all the Bishops, to be permanently added at the end of the Anathemas listed in the "Rite of Orthodoxy," celebrated on the First Sunday of the Great Fast, the Sunday of Orthodoxy is sobering indeed for the Russian Orthodox faithful for whose protection it was enacted:
"To those who attack the Church of Christ by teaching that Christ's Church is divided into so-called "branches" which differ in doctrine and way of life, or that the Church does not exist visibly, but will be formed in the future when all "branches" or sects or denominations, and even religions will be united into one body; and who do not distinguish the Priesthood and Mysteries of the Church from those of the heretics, but say that the baptism and Eucharist of heretics is effectual for salvation; therefore, to those who knowingly have communion with these aforementioned heretics or who advocate, disseminate, or defend their heresy of ecumenism under the pretext of brotherly love or the supposed unification of separated Christians, Anathema!"
The so-called “lifting of anathemas” even though the differences have grown consistently since the Great Schism. More recent events like forbidden concelebrations and joint prayers with known heretics, various “statements” such as the Chambesy Agreement, Balamand, Canberra, the agreement in New York, and the Toronto statement continue to confuse and blur the lines between Truth and falsehood.
The Moscow Patriarchate in recent years has made much clear for the Orthodox faithful under her care. In the profound document entitled, “The Basic Principles of Attitude to the Non-Orthodox”, we have the following:
2.4. The Orthodox Church cannot accept the assumption that despite the historical divisions, the fundamental and profound unity of Christians has not been broken and that the Church should be understood as coextensive with the entire “Christian world”, that Christian unity exists across denominational barriers and that the disunity of the churches belongs exclusively to the imperfect level of human relations. According to this conception, the Church remains one, but this oneness is not, as it were, sufficiently manifest in visible form. In this model of unity, the task of Christians is understood not as the restoration of a lost unity but as the manifestation of an existing unity. This model repeats the teaching on “the invisible Church” which appeared during the Reformation.
2.5. The so-called “branch theory”, which is connected with the conception referred to above and asserts the normal and even providential nature of Christianity existing in the form of particular “branches”, is also totally unacceptable.
2.6. Orthodoxy cannot accept that Christian divisions are caused by the inevitable imperfections of Christian history and that they exist only on the historical surface and can be healed or overcome by compromises between denominations.
2.7. The Orthodox Church cannot recognize “the equality of the denominations”. Those who have fallen away from the Church cannot re-unite with her in their present state. The existing dogmatic differences should be overcome, not simply bypassed, and this means that the way to unity lies through repentance, conversion and renewal.