The Orthodox teaching of the Church, which in itself is quite clear and rests upon Sacred Scripture and Sacred Tradition, is to be contrasted with another concept which is widespread in the contemporary Protestant world and has penetrated even into Orthodox circles. According to this different concept, all the various existing Christian organizations, the so-called "confessions" and "sects," even though they are separated from each other, still comprise a single "invisible Church," inasmuch as each of them confesses Christ as Son of God and accepts His Gospel.
The dissemination of such a view is aided by the fact that side by side with the Orthodox Church there exists outside of her a number of Christians that exceeds by several times the number of members of the Orthodox Church. Often we can observe in this Christian world outside the Church a religious fervor and faith, a worthy moral life, a convictionall the way to fanaticismof one's correctness, an organization and a broad charitable activity. What is the relation of all of them to the Church of Christ?
Of course, there is no reason to view these confessions and sects as on the same level with non-Christian religions. One cannot deny that the reading of the word of God has a beneficial influence upon everyone who seeks in it instruction and strengthening of faith, and that devout reflection on God the Creator, the Provider and Saviour, has an elevating power there among Protestants also. We cannot say that their prayers are totally fruitless if they come from a pure heart, for in every nation he that feareth Him... is accepted with Him (Acts 10:3-5). The Omnipresent Good Provider God is over them, and they are not deprived of God's mercies. They help to restrain moral looseness, vices, and crimes; and they oppose the spread of atheism.
But all this does not give us grounds to consider them as belonging to the Church. Already the fact that one part of this broad Christian world outside the Church, namely the whole of Protestantism, denies the bond with the heavenly Church, that is, the veneration in prayer of the Mother of God and the saints, and likewise prayer for the dead, indicates that they themselves have destroyed the bond with the one Body of Christ which unites in itself the heavenly and the earthly. Further, it is a fact that these non-Orthodox confessions have "broken" in one form or another, directly or indirectly, with the Orthodox Church, with the Church in its historical form; they themselves have cut the bond, they have "departed' from her. Neither we nor they have the right to close our eyes to this fact.
The teachings of the non-Orthodox confessions contain heresies which were decisively rejected and condemned by the Church at her Ecumenical Councils. In these numerous branches of Christianity there is no unity, either outward or inwardeither with the Orthodox Church of Christ or between themselves. The supra-confessional unification (the "ecumenical movement!') which is now to be observed does not enter into the depths of the life of these confessions, but has an outward character. The term " invisible" can refer only to the Heavenly Church. The Church on earth, even though it has its invisible side, like a ship a part of which is hidden in the water and is invisible to the eyes, still remains visible, because it consists of people and has visible forms of organization and sacred activity.
Therefore it is quite natural to affirm that these religious organizations are societies which are "near," or "next to," or " close to," or perhaps even" adjoining" the Church, but sometimes " against" it; but they are all "outside" the one Church of Christ. Some of them have cut themselves off, others have gone far away. Some, in going away, all the same have historical ties of blood with her; others have lost all kinship, and in them the very spirit and foundations of Christianity have been distorted. None of them find themselves under the activity of the grace which is present in the Church, and especially the grace which is given in the Mysteries of the Church. They are not nourished by that mystical table which leads up along the steps of moral perfection.
The tendency in contemporary cultural society to place all confessions on one level is not limited to Christianity; on this same all-equalling level are placed also the non-Christian religions, on the grounds that they all "lead to God," and besides, taken all together, they far surpass the Christian world in the number of members who belong to them.
All of such "uniting" and "equalizing" views indicate a forgetfulness of the principle that there can be many teachings and opinions, but there is only one truth. And authentic Christian unityunity in the Churchcan be based only upon oneness of mind, and not upon differences of mind. The Church is the pillar and ground of the Truth (I Tim. 3:15).
From Orthodox Dogmatic Theology, trans. by Fr. Seraphim Rose (Platina, CA: St. Herman of Alaska Brotherhood, 1994), pp. 243-246. See also "Attributes of the Church," by St. Justin (Popovich) of Chelije.