By Father Edward McNamara, Professor of Liturgy, Regina Apostolorum Pontifical University
In the early Church the readings were usually organized on a simple basis of continuity; that is, they took off from where they had finished the previous Sunday.
As the liturgical year developed, certain readings began to be reserved for certain feast days and seasons and so a thematic cycle developed.
When the Second Vatican Council asked for the selection of readings used at Mass to be increased, the experts took inspiration from the two ancient methods of continuity and thematic readings.
For Sundays they developed a three-year cycle, one for each synoptic gospel: A for Matthew, B for Mark (with five readings from St. John, Chapter 6, inserted after the 16th Sunday), and C for Luke. So during Ordinary time each Sunday Gospel continues on from the previous week.
The New Testament readings also follow this continual system, the Letters of St. Paul and St. James being read during Ordinary time because those of John and Peter are read during Christmas and Easter.
This continuous system is why they do not always seem to fit in well with the Gospel.
The Old Testament reading (or the Acts of the Apostles during Eastertide) and the responsorial psalm are chosen so as to somehow relate to the Gospel text.
During Advent, Christmas, Lent and Easter and on solemnities all three readings are chosen so as to highlight the particular spiritual message of the season.
With respect to the daily readings: during Ordinary time all four Gospels are read using a semi-continual system during the course of the year. Mark weeks 1-9; Matthew 10-12; and Luke 22-34.
St. John’s Gospel is read semi-continuously, above all, during part of Lent and almost all of Eastertide on both Sundays and weekdays.
Thus almost all of Mark 1-12 is read, then the texts of Matthew and Luke that are not found in Mark.
The first daily reading, taken from either Testament, also uses a semi-continuous system organized in a two-year cycle for odd and even numbered years.
The New Testament readings offer the substance of almost all the letters whereas the Old Testament readings offer a selection of the most important elements of each book. Almost all of the books are represented except some brief prophets and the Song of Songs.
Toward the end of the year the reading come from Revelation and Daniel, which fit well with the apocalyptic sermons from Luke.
Unlike the readings for ordinary time the daily readings of Advent, Christmas, Lent and Easter have been chosen to relate to each other and to reflect the liturgical season.
A special characteristic of Eastertide is the reading from the Acts of the Apostles as first reading every day.
They also repeat the same readings each year and are not divided into an even-odd cycle.
[Originally posted on Zenit]