St. Cyril of Jerusalem's Catechetical Lectures are 23 pivotal 4th-century talks for catechumens (new converts) in Jerusalem, covering core Christian doctrine (God, Trinity, Christ, Creed) in the first 18, followed by 5 Mystagogical Catecheses on the Sacraments (Baptism, Confirmation, Eucharist) for the newly baptized, offering an invaluable, warmly pastoral glimpse into early church teaching and practice.