This book presents three patristic texts on the Priesthood and the Holy Eucharist by Saint Symeon of Thessalonica (A Discourse on the Priesthood to a Pious Monk, who Had Become a Deacon and Priest and Later Became a High Priest), Patriarch Kallinikos of Constantinople (A Guide for Priests and Deacons on How They Must Serve in the Church, How They Should Prepare for the Sacred Service of the Divine Liturgy, and How They Should Amend Sudden Eventualities and Difficulties that Emerge in the Course of Rendering such a Service) and Saint Mark Eugenikos of Ephesus (Exposition of the Church's Acolouthy). These texts serve as a reminder to clergy and laity that prayer and liturgy are primary functions of priests and are designed to put forward in a constant way the Mystery of Christ, which constitutes the basis of the Church as the Arc of salvation.