[quote="squain, post:1, topic:236205"]
I recently heard that the scripture readings during mass are the same across the world each Sunday. I find this truly remarkable...
Does anyone know if the readings are intended to cover the entire Bible eventually, or are they pulled from selected books? If they do cover the entire Bible, how long does it take to get through the entire cycle of reading all the books (years, I presume), or are the readings not really that cyclical?
Basically I'd like to know more about how the readings are chosen, and what system the church uses to choose them each Sunday.
You must remember first that the whole three-year cycle is a relatively recent development within the Church. The more ancient custom (as you'll observe if you look across the lectionaries of different Churches) is to have a cycle of readings that apparently last only for a single liturgical year before it repeats again: such was the case in the Roman Rite before the Ordo Lectionum Missae or 'Order of the Readings for Mass' was promulgated post-Vatican II. The Eastern Churches (Eastern Orthodox, Oriental Orthodox, Byzantine Catholic, the Assyrian Church of the East, and those bodies not in communion with any of them but still practicing eastern liturgical customs) tend to retain the use of a one-year lectionary in their liturgies even today.
At least within the Roman Church (as well as some Protestant churches which use the * Revised Common Lectionary* and its deritatives, which are based from the new order promulgated after Vatican II) nowadays, the Order of Readings are organized into three-year cycles of readings for Sundays. The years are designated as Year A, B, or C. Every yearly cycle, which begins on the first Sunday of Advent, is assigned a Synoptic Gospel of its own (John is read throughout certain liturgical seasons, such as the whole of Easter, as well as Advent, Christmas, and Lent where appropriate): A is Matthew, B is Mark, and C is Luke.
Aside from this three-year cycle, we also have a two-year cycle for weekday Mass (called Cycle I and Cycle II). Odd-numbered years are Cycle I; even-numbered ones are Cycle II. The weekday lectionary includes a reading from the Old Testament, Acts, Revelation, or the Epistles, a responsorial Psalm, and a reading from one of the Gospels. These readings are generally shorter than those appointed for use on Sundays. The Gospels are arranged so that portions from all four are read every year.
Of course, including 100% of the Bible is impossible (considering some parts are, admittedly, dull reading unless you're an ancient Israelite, such as genealogies or most of Leviticus :D), but an estimate by Fr. Felix Just gives out a total of 13.5% for the Old Testament and 71.5% of the New Testament, Sunday and weekday readings combined.