The apostle Paul, comparing the life of the Church of Christ with a marriage, or with the relationship between a man and wife, concludes his thoughts with these words: This is a great mystery: but I speak concerning Christ and the church (Eph. 5:32). The life of the Church in its essence is mystical; the course of its life cannot be entirely included in any “history.” The Church is completely distinct from any kind whatever of organized society on earth.
Fr. Michael Pomazansky, Orthodox Dogmatic Theology, p. 224
Over the past several years the Lord has increasingly deepened my love for church history- especially the patristic period. This caveat from from Pomazansky is well taken though. In its essence the church is spiritual. But its reality is manifested through physical entities- individual churches and “collections” of churches, i.e. denominations. The best church history can only describe the physical manifestation of the church and with that description hope to capture some of the spiritual reality.
This is a great mystery.