A Lectionary provides the readings and the responsorial psalm assigned for each Mass of the year (Sundays, weekdays, and special occasions). The readings are divided by the day or the theme (baptism, marriage, vocations, etc.) rather than according to the books of the Bible. Introductions and conclusions have been added to each reading. Not all of the Bible is included in the Lectionary.
Individual readings in the Lectionary are called pericopes, from a Greek word meaning a "section" or "cutting." Because the Mass readings are only portions of a book or chapter, introductory phrases, called incipits, are often added to begin the Lectionary reading, for example, "In those days," "Jesus said to his disciples," etc.