Lectionary

This book contains stories, teachings, and songs from the Bible that have been chosen by the Church to be proclaimed and that can be read (or sung) by a priest, deacon, or trained lay minister.

At Sunday Mass, we have a First Reading, Responsorial Psalm, Second Reading, and Gospel. A lay reader will generally proclaim the First Reading, Responsorial Psalm and Second Reading. The Gospel must be proclaimed by a deacon or a priest.

Our entire Lectionary contains about:

90% of Gospel Accounts from the Bible
55% of Acts, Epistles, and Revelation
13.5% of the Old Testament

This was a substantial improvement from the amount of Scriptures heard at Mass before Vatican II, at which time the Lectionary included approximately 22% of the Gospels, eleven precent of the Epistles and less than one percent of the Old Testament (other than the psalms).

Source: The Word of the Lord at Mass: Understanding the Lectionary by Regina A. Boisclair, Liturgy Training Publications, 2015