Today: "The Expectation of the Parturition of the Blessed Virgin Mary"

A little feast from the old Calendar.

The feast or commemoration seems to have originated in Spain, establishing the Marian character of Advent, if you will.  The Expectation of the Birth of the Lord, pondered by Mary ever virgin, Mother of God.  

This Feast, which sometimes goes under the name of Our Lady of O, or the Feast of O, on account of the great antiphons which are sung during these days, and, in a special manner, of that which begins O Virgo virginum (which is still used in the Vespers of the Expectation—see below, together with the O Adonai, the antiphon of the Advent Office), was kept with great devotion in Spain. - Adapted from The Liturgical Year by Abbot Gueranger

The Marian character of Advent.

The Expectation says it all, Our Lady expected the Messiah, as revealed to her by the Angel Gabriel.  It makes me think, how in our times we are in a sort of Marian era.  As if Our Lady is calling us to expect the Messiah, the return of Christ.  She exemplifies the conduct and disposition of soul we ought to cultivate in ourselves.  Full of hope, with a love 'beyond all telling', going within to meet him.  I don't know, of course, but it is good for me to take refuge in Our Lady.

"The Virgin, weighed
With the Word of God
Comes down the road:
If only you will shelter her." - John of the Cross 

From Marialis Cultus.

3. During Advent there are many liturgical references to Mary besides the Solemnity of December 8, which is a joint celebration of the Immaculate Conception of Mary, of the basic preparation (cf. Is. 11:1, 10) for the coming of the Savior and of the happy beginning of the Church without spot or wrinkle.[11] Such liturgical references are found especially on the days from December 17 to 24, and more particularly on the Sunday before Christmas, which recalls the ancient prophecies concerning the Virgin Mother and the Messiah[12] and includes readings from the Gospel concerning the imminent birth of Christ and His precursor.[13]

4. In this way the faithful, living in the liturgy the spirit of Advent, by thinking about the inexpressible love with which the Virgin Mother awaited her Son,[14] are invited to take her as a model and to prepare themselves to meet the Savior who is to come. They must be “vigilant in prayer and joyful in…praise.”[15] We would also remark that the Advent liturgy, by linking the awaiting of the Messiah and the awaiting of the glorious return of Christ with the admirable commemoration of His Mother, presents a happy balance in worship. This balance can be taken as a norm for preventing any tendency (as has happened at times in certain forms of popular piety) to separate devotion to the Blessed Virgin from its necessary point of reference — Christ. It also ensures that this season, as liturgy experts have noted, should be considered as a time particularly suited to devotion to the Mother of the Lord. This is an orientation that we confirm and which we hope to see accepted and followed everywhere. - St. Paul VI, Marialis Cultus