What is the lectionary, and how are the Sunday readings chosen?

The lectionary is the liturgical book containing the Scripture readings proclaimed at Mass and other Catholic services. Sunday readings are assigned by the Church according to the liturgical season, feast, and a repeating cycle, rather than selected freely each week.

What the lectionary contains. At a typical Sunday Mass, the lectionary provides a first reading, a responsorial psalm, a second reading, and a Gospel. During most of the year, the first reading comes from the Old Testament. During the Easter season, it generally comes from Acts. The second reading usually comes from an apostolic letter or Revelation. The Gospel has the place of highest honor because it directly proclaims the words and deeds of Christ. Scripture is an integral part of the liturgy, and Christ is present in His word when it is proclaimed in the Church (CCC 1088, 1154).

How Sundays are arranged. In the current Roman Rite, Sunday readings follow a three-year cycle:

1. Year A centers mainly on Matthew.
2. Year B centers mainly on Mark.
3. Year C centers mainly on Luke.

John is read during major seasons and at selected points in all three years. For example, the Bread of Life discourse from John 6 appears during Year B. The cycle begins with the First Sunday of Advent, not January 1.

How the readings relate. The first reading is often chosen because it has a direct connection with the Gospel, such as prophecy and fulfillment. The responsorial psalm answers the first reading in prayer. In Ordinary Time, the second reading commonly follows a semi-continuous course through a New Testament letter, so it may not have an obvious theme connecting it to the Gospel. During Advent, Christmas, Lent, Easter, and solemnities, all the readings more closely express the mystery being celebrated.

Why the Church uses a set plan. A lectionary protects the congregation from hearing only a preacher's favorite passages. Following the Second Vatican Council, the Roman lectionary was expanded so that a richer portion of Scripture would be presented to the faithful (Sacrosanctum Concilium 51). The Holy Spirit uses this proclaimed word to awaken faith, prepare the congregation for the Eucharist, and call forth a response of prayer and obedience (CCC 1100-1102).

Before Sunday Mass, read the assigned passages slowly and notice how the first reading and psalm illuminate the Gospel. The readings can be found in a parish missal, a Catholic calendar, or the website of the bishops' conference.