Wikipedia : Lectionary
A Lectionary is a book or listing that contains a collection of scripture readings for Christian worship.
Throughout history, many varying lectionaries have been used in different parts of the Christian world.
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Since the Second Vatican Council, the revised lectionary of the Roman Catholic Church has been a foundation block upon which many contemporary lectionaries have been based. Most of the current lectionaries used by western Christian denominations organize the scripture passages to be read in worship services for each week of the year. The listing for a given week includes:
A reading from the Hebrew Scriptures;
A Responsorial Psalm;
A reading from one of the Epistles;
A reading from one of the Gospels.
The Lectionary is generally organized into a three-year cycle of readings. The first three readings change from week to week to complement the Gospel reading. The Gospel reading is coordinated with the day's observance according to the Liturgical calendar; during common time the Gospel reading is usually chronological from week to week or grouped thematically by teaching. The reading cycle is denoted by letter as:
Year A: Readings from the Gospel of Matthew.
Year B: Readings from the Gospel of Mark.
Year C: Readings from the Gospel of Luke.
The Gospel of John is always read for Easter, and is utilized for other liturgical seasons including Advent, Christmas, and Lent where appropriate.
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