We use the reading cycle known as the “Revised Common Lectionary.” Many denominations throughout the world use this same 3 year readings cycle that was published in 1994 in an ecumenical, collaborative effort. The tradition for appointed worship texts arises out of the Jewish custom of particular Torah and prophetic readings. By the year 380, the Christian pilgrim Egeria, on her pilgrimage to Jerusalem during Holy Week, noticed that churches there used the same readings as in her home church!
Revised Common Lectionary Sundays and Principle Festivals
This lectionary provides a three-year series of readings for Sunday starting with the season of Advent, four weeks before Christmas Day. For each Sunday and festival, three readings and a psalm are suggested and include: a Gospel reading, an Old Testament reading, and a New Testament reading. The lectionary is a work of The Consultation on Common Texts, an ecumenical consultation of liturgical scholars and denominational representatives from the United States and Canada, who produce liturgical texts for use in common by North American Christian Churches.
Each year of the Revised Common Lectionary centers on one of the synoptic Gospels — Matthew, Mark and Luke. The Gospel of John is read periodically in all three years and is especially frequent in Year B.
Year A focuses on the Gospel of Matthew. The semicontinuous Old Testament readings focus on major Genesis narratives, the covenant with Moses, and the establishment of Israel in the Promised Land. The second, New Testament, readings are from Romans, Philippians and 1 Thessalonians.
Year B focuses on the Gospel of Mark with more selections from the Gospel of John than any other year. The semicontinuous readings from the Old Testament focus on the covenant of David and Wisdom literature. The second, New Testament, readings are from 1 and 2 Corinthians, Ephesians, James and Hebrews.
Year C focuses on the Gospel of Luke. The semicontinuous Old Testament readings are of prophetic proclamation chosen in chronological order and highlighting Jeremiah. The second, New Testament, readings are chosen mainly from Galatians, Colossians, 1 and 2 Timothy and 2 Thessalonians. (Note: there is no link for Year C at this point)
For much of the year, the Old Testament lesson is closely related to the Gospel reading. However, from the first Sunday after Trinity Sunday to the end of the church year, two provisions have been made: a continuation of the complimentary readings or a semicontinuous pattern of Old Testament readings. – See fuller description here.