There is one body and one Spirit, just as you were called to the one hope that belongs to your call, one Lord, one faith, one baptism, one God and Father of us all, who is above all and through all and in all. (Ephesians 4:4-6)
Bishop Kallistos Ware writes:
As St. Ignatius insisted, “Take care to participate in one Eucharist: for there is one flesh of our Lord Jesus Christ, and one cup for union in His blood, and one altar, just as there is one bishop.” The repetition of the word “one” is deliberate and striking: “one Eucharist…one flesh…one cup…one altar…one bishop.” Such is St. Ignatius’ understanding of the Church and its unity: the Church is local, an assembly of all the faithful in the same place (epi to avto); the Church is Eucharistic, a gathering around the same altar to share in a single loaf and a single cup; and the Church is hierarchical—it is not simply any kind of Eucharistic meeting, but it is that Eucharistic meeting which is convened under the presidency of the one local bishop.
Church unity, as the Bishop of Antioch envisages it, is not merely a theoretical ideal but a practical reality, established and made visible through participation of each local community in the Holy Mysteries. Despite the central role exercised by the bishop, unity is not something imposed from outside by power of jurisdiction, but it is created from within through the act of receiving communion. The Church is above all else a Eucharistic organism which becomes itself when celebrating the sacrament of the Lord’s Supper “until He comes again” (I Cor 11:26). (The Inner Kingdom, p. 17)