The common readings of the Catholic sass are all passages taken from the Bible. Sunday services and masses on Holy Days of Obligation have two readings prior to the reading of a passage taken from the Gospels. The weekday masses omit the second reading, moving directly to the Gospels passage.
The Catholic Church uses between two and three passages from the Bible for the common readings and additional passages for other aspects of the mass. The reading order for Sunday mass is typically a passage from the Old Testament, a passage from the New Testament and then a reading from the Gospels. During weekday mass omits one of the two readings, as proscribed by the Lectionary, but never the reading from the Gospels.