What is the Lectionary? 

The Lectionary, or sacred book of texts out of which we read at every Mass, is 85% of the Bible organized by Scripture scholars for proclamation at weekday and Sunday Masses. Did you know that there are three cycles of readings at Eucharist called calendar cycles? They are called years A, B and C. They comprise three years of readings. The gospels of each year follow either Matthew, Mark or Luke with John interspersed in between. The first reading is chosen in connection to the gospel and often follows, however incompletely, a book of the Old Testament (in Easter and Pentecost, the first reading is almost exclusively from the New Testament). This is called semi-continuous reading. Most Protestant churches follow our Catholic lectionary, with minor adaptations. Here is a link to a further explanation of Lectionary cycles and how they intertwine with church seasons such as Lent, Advent, and Ordinary Time: http://catholic-resources.org/Lectionary/index.html