The Nicene-Constantinople Creed speaks of one Church. Yet there are many Christian confessions in the world that call themselves churches. It is not uncommon for these confessions to refuse each other Holy Communion and even to be mutually hostile. Do these things destroy the unity of the Church? Is it not the case that a formerly single Church has disintegrated into various denominations and lost its unity?

To begin with, it should be pointed out that according to Orthodox ecclesiology the Church by her very nature is indivisible and will remain so until the end of the age. The divisions and schisms resulting from heresy did not entail the dismembering of the Church, but rather the falling away of heretics from the single organism of the Church and the loss of communion with her. As mentioned above, heresy is characterized by the way it consciously opposes universal church doctrine.

Orthodoxy does not concur with the ‘branch theory’, according to which all the existing Christian denominations are branches of the one tree. The unity of the Church is conditioned by unity around the Eucharist: outside of eucharistic communion there can be no unity. We pray at the Liturgy of St. Basil the Great, ‘And unite all of us to one another who become partakers of the one Bread and Cup in the communion of the Holy Spirit’. Belonging to the Church is expressed not only in being in dogmatic unity with her, but also in the unity of the Eucharist. It is precisely as dismembered branches that the Church regards those Christian groups who have opposed accepted church teaching through heresy.

Does this necessarily mean that the Orthodox should regard all non-Orthodox Christian confessions as heretical gatherings or withered branches cut off from the trunk? For some Orthodox theologians this is certainly the case. Yet the official position of most Orthodox Churches is, as a rule, much more open towards other Christian confessions, especially those whose ecclesiology is identical or close to that of the Orthodox: the Catholic Church and the Oriental Orthodox (pre-Chalcedonian) Churches.

The early Church took a strict line with heretics: the church canons not only forbid them from taking part in the Eucharist, but also forbid people from praying with heretics. However, we must remember that the heresies of the first Christian centuries (Arianism, Sabellianism, and Eutychian Monophysitism) rejected the very foundations of the Christian faith: the Divinity of Christ, the equality of the Persons of the Trinity, the fulness of the divine and human natures of Christ. This cannot be said of the majority of today’s Christian confessions for they accept the basic dogmas of the Church. Orthodox Christians, therefore, ought to make a distinction between non-Orthodoxy and heresy. St. Philaret of Moscow believed that placing Catholicism and Arianism on an equal footing is ‘both rigorous and counterproductive’. Even more counterproductive is applying what was said by the Ecumenical Councils on the excommunication of heretics to contemporary non-Orthodox Christians.

When dealing with the difficult question of Christian divisions, the Orthodox may wish to bear in mind that God alone knows where the limits of the Church are. As St. Augustine said, ‘many of those who on earth considered themselves to be alien to the Church will find that on the day of Judgment that they are her citizen; and many of those who thought themselves to be members of the Church will, alas, be found to be alien to her’. To declare that outside of the Orthodox Church there is not and cannot be the grace of God would be to limit God’s omnipotence, to confine Him to a framework outside of which He has no right to act.