“The Church is one not only inwardly, but also outwardly. Outwardly its unity is manifested in the harmonious confession of faith, in the oneness of Divine services and Mysteries, in the oneness of the grace-giving hierarchy, which comes in succession from the Apostles, in the oneness of canonical order. The Church on earth has a visible side and an invisible side. The invisible side is: that its Head is Christ; that it is animated by the Holy Spirit; that in it is performed the inward mystical life in sanctity of  the more perfect of its members. However, the Church, by the nature of its members, is visible, since it is composed of men in the body; it has a visible hierarchy; it performs prayers and sacred actions visibly; it confesses openly by means of words, the faith of Christ.”
(Fr. Michael Pomazansky, Orthodox Word Vol 1 #10)