The work of the famous Russian historian of the Christian church has long become classical, although it remained little known to a wide range of readers. It is distinguished by a deep penetration into the essence of the historical development of the church with the complex and contradictory dynamics of the formation of dogma, the structure of organization, canonical rules, liturgics and mysterious practice. The author on historical, linguistic and theological material reveals the complexity and inexhaustibility of the patristic heritage of the first ten centuries (before the schema of 1054) of church history, when the foundations of churchiness were laid, which determines the life of Christianity today.