The Lectionary
The traditional cycle of Scripture readings by which the Church has read through the Bible in worship, week by week, since antiquity.
The lectionary is one of the oldest features of Christian worship. In the ancient Church, Justin Martyr describes the reading of "the memoirs of the apostles or the writings of the prophets, as long as time allows" on the Lord's Day. From those beginnings the Church has kept an ordered cycle of readings.
Two lectionaries dominate today: the Revised Common Lectionary (3-year cycle, used by many Protestant, Anglican, and Roman Catholic churches), and the historic one-year lectionary (used by the Eastern Orthodox and the traditional Lutheran and Anglican liturgies). Both aim at the same thing — that the whole of Scripture, in its proper proportion, would be heard aloud in worship over time.