This is the fourth volume of a detailed and systematic exposition of the history, canonical structure, doctrine, moral and social teaching, liturgical services, and spiritual life of the Orthodox Church. The purpose of this series is to present Orthodox Christianity as an integrated theological and liturgical system, in which all elements are interconnected. “Orthodox worship is precious in that it provides the clear standard of Orthodoxy as a mode of thinking and a way of life” (p. XXX). This has been the law of the Church from ancient times: lex orandi, lex credendi, “the law of prayer is the law of faith.”