This entry is updated from last year. Today, December 18, is a feast of long standing in the Latin Church. Though its Mass and office will not be offered liturgically in most places (owing to its not being a universal feast), the “Expectation of the Blessed Virgin Mary” has origins going back at least to seventh-century Spain.
The Catholic Encyclopedia has a small entry on the feast. It tells us of the peculiar name the feast was given in Spain:
The feast of 18 December was commonly called, even in the liturgical books, “S. Maria de la O,” because on that day the clerics in the choir after Vespers used to utter a loud and protracted “O,” to express the longing of the universe for the coming of the Redeemer (Tamayo, Mart. Hisp., VI, 485). The Roman “O” antiphons have nothing to do with this term, because they are unknown in the Mozarabic Rite. This feast and its octave were very popular in Spain, where the people still call it “Nuestra Señora de la O.”
The O Antiphons are works of surpassing beauty in themselves, and worthy of meditation during these days. That they have no formal connection to this Marian feast of Advent affirms all the more the common root of O in these liturgical usages. This common root is the exclamation O as an expression of longing, a sigh of the heart of ancient Israel for the coming of the Redeemer. And during Advent’s four weeks, we Christians put ourselves in the place of the Old Testament faithful who, for four thousand years (according to the Vulgate chronology) awaited the coming (advent) of the Messias. As a cry of eager anticipation, the O has an affinity for that other word we see all over the Advent liturgy (including in the O Antiphons): Veni! (come).
And who better than Mary to show us how to expect Jesus’ coming? She who, in the penetrating phrase of Saint Augustine, “conceived Christ in her mind before conceiving Him in her body,” is the perfect model of holy “great expectations.”
Sancta Maria de la O, ora pro nobis!