For centuries, churches have used lectionaries to guide the structure and content of their worship. In the most general terms, lectionaries provide pre-selected sets of Scripture readings for use at specific times. One of the most commonly used lectionaries for Western Christians is the Revised Common Lectionary (RCL), a three-year cycle of scriptures that's aligned with the traditional church calendar. It is applied more or less strictly depending on the denomination and local congregation’s styles. Throughout the year, the RCL offers four Scripture passages for each week: two from the Old Testament (always including a Psalm) and two from the New (always including a passage from one of the Gospels).