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. Volume One focused on the history and canonical structure of the Orthodox Church; Volume Two on the fundamental teachings of the Church, grounded in Scripture and Tradition; Volume Three on the unique aspects of Orthodox art as expressed in its architecture, icons, and liturgical music. In Volume Four the history, structure, and meaning of the Church's liturgical services-including the daily, weekly, yearly, and festal cycles-are explored and explained. Both beginners and experts can benefit from this thorough examination of Orthodox worship and liturgical life. In the services of the Church, heaven and earth meet. As St Vladimir's envoys to Constantinople said, "We knew not whether we were in heaven or earth.... We only know that God dwells among men. We cannot forget that beauty."