Earlier this year, I downloaded a new calendar into my online calendar app. It is a calendar that identifies each Sunday in the church’s liturgical year (First Sunday in Advent, Second Sunday in Epiphany, Ninth Sunday after Pentecost, and so on), as well as other significant days (Ash Wednesday, Good Friday, Ascension Day, and others).
It also provides the four readings that the Revised Common Lectionary provides for each Sunday, as well as for those additional liturgical days. It is a useful resource to have on hand! The calendar identifies each Sunday with a light blue band across the name, and sits alongside other calendars (with other colour-codings) that identify Public Holidays, Birthdays, Work commitments, and other specialised matters.
But look what it has done for December 24, which we all know is Christmas Eve: it has provided no less than three entries for the one day!

Why are there three different sets of readings for the “Nativity of the Lord” (aka Christmas)? I hunted through some church web sites, and found that it is because of developments way back before the so-called Middle Ages … back in the days when Christianity was still developing and evolving and finding its place in society.
What follows is asked on what I found at https://www.catholicculture.org/culture/library/view.cfm?recnum=7399 … I am assuming that this is accurate!
The simple explanation is that three different services of worship relating to “the nativity of the Lord” developed over time within Rome, and, rather than one replacing another, each was added, each having its own focus and also being held at a different location.
Catholic Culture says that “the first Mass originally was connected with the vigil service at the chapel of the manger in the church of St. Mary Major in Rome”; it was a small service at midnight which Pope Sixtus III began in 440CE. This has continued as the first service, Proper I in the Revised Common Lectionary.

The second Mass, we are advised, was “the public and official celebration of the feast, held on Christmas Day at the church of St. Peter, where immense crowds attended the pope’s Mass and received Communion”. That continues to this day, when the Pope appears on a balcony overlooking the packed square outside St Peter’s.
Catholic Culture advises, however, that “under Pope Gregory VII (1085) the place of this Mass was changed from St. Peter’s to St. Mary Major, because that church was nearer to the Lateran Palace (where the popes lived). It forms Proper III in the Revised Common Lectionary.

The third service to develop is actually the “middle service”, or Proper II in the Revised Common Lectionary. Catholic Culture explains: “In the fifth century, the popes started the custom of visiting at dawn, between these two services, the palace church of the Byzantine governor. There they conducted a service in honor of Saint Anastasia, a highly venerated martyr whose body had been transferred from Constantinople about 465 and rested in this church which bore her name.”
This was a popular service, because Saint Anastasia was widely venerated in the Roman Empire; in later centuries, as the empire dissolved and Anastasia receded in significance, this middle service was still retained, and another Mass of the Nativity was held. This became the second of the three Masses on Christmas Day.

The Roman Missal has shaped the liturgy for each of these services to highlight different elements of the Christmas story. Thus, “the first Mass honors the eternal generation of the Son from the Father, the second celebrates His incarnation and birth into the world, the third His birth, through love and grace, in the hearts of men [sic.]”.
The Gospel passage set for each Mass—reflected in the Gospel passages proposed by the Revised Common Lectionary—has led to the popular name for each service. Proper I offers Luke 2:1–14, which tells of the birth of Jesus and the angelic announcement to the shepherds in the fields; thus, people came to call the first Mass Angels’ Mass. Proper II proposes Luke 2:8–20, when the shepherds visit the newborn child and his parents; accordingly, it became known as the Shepherds’ Mass.
Proper III takes us to the majestic prologue to John’s Gospel, John 1:1–14, which tells in beautiful poetry of the coming of The Word, who takes on human flesh to live amongst us; this then characterises this service as the Mass of the Divine Word.
The three readings from the Epistles contain excerpts with short credal-like affirmations: “the manifestation of the glory of our great God and Saviour” (Titus 2:11–14), “when the goodness and lovingkindness of God our Saviour appeared” (Titus 3:4–7), and the statement that “in these last days [God] has spoken to us by a Son”, whose nature is explicated by a string of Hebrew Scripture citations (Heb 1:1–12). Each of these fits well for Christmas celebrations.
Likewise, the three Hebrew Scripture passages themselves orient us towards God’s actions within human history. For Proper I, First Isaiah speaks about the child to be born, to be named “Wonderful Counsellor, Mighty God, Everlasting Father, Prince of Peace” (Isaiah 9:2–7). For Proper II, Third Isaiah declares, “the Lord has proclaimed to the ends of the earth, ‘see, your salvation comes’” (Isaiah 62:6–12). And for Proper III, Second Isaiah rejoices in “the messenger who brings good news, who announces salvation”, through whom “all the ends of the earth shall see the salvation of our God” (Isaiah 52:7–10).
Each prophetic passage, seen through the eyes of Christian faith, reflects the divine intention, made clear through Jesus, to offer salvation to every person on earth—prefiguring the good news of Jesus out of the different contexts of pre-exiling Israel (Isa 9), the hard years of Exile (Isa 52), and the time of rebuilding after that exile experience (Isa 62).
Finally, the psalms selected for these three services (Psalms 96, 97, and 98) contribute strongly to the joyful ethos of the Christmas celebrations, with the injunction to “sing to the Lord a new song” (96:1, 98:1) and “worship the Lord in the splendour of holiness” (96:9), singing praises (98:4–6) and rejoicing (96:11–12; 97:8, 12; 98:8), celebrating that “the Lord is king” (97:1) and “exalted overall gods” (97:9) and rejoicing that “the Lord, he is coming, coming to judge the earth … with righteousness, and with truth” (96:13; 97:2; 98:9). These are notes that are entirely appropriate and fitting for the joyful celebrations of Christmas!
