Nativitatem Virginis Mariae celebremus; Christum eius Filium adoremus Dominum ("Let us celebrate the Nativity of the Virgin Mary; let us adore Christ the Lord her Son").
With that ancient Invitatory, the Church still summons us today to celebrate the birth of the Blessed Virgin Mary. Most saints are commemorated only on the day of their death. But, conceived without sin, Mary's earthly birth is also honored in the Church's calendar (as is also that of John the Baptist, who is understood to have been sanctified before birth at the time of the Visitation (cf. Luke 1:15).
Historical details about the circumstances of Mary's birth are, of course, largely lacking. Devotion has had to make due with ancient legends recounted in the 2nd-century Protoevangelium of James, from which we learn, for example, the traditional names ascribed to Mary's parents, Anne and Joachim. A 5th-century basilica, built in Jerusalem on the supposed site of their home (and thus of Mary's birth) was dedicated on this date. Hence, today's feast, which eventually made its way west to 7th-century Rome The gospel for this feast remains Matthew's genealogy of Jesus, tracing his lineage from Abraham through David to Joseph, Mary's husband. The traditional 1st reading used to be Proverbs 8:22-35, in which Wisdom is portrayed as speaking of herself as the first-born of his ways and the forerunner of his prodigies. The modern, Paul VI Lectionary has largely abandoned the old tradition of applying passages from the sapiential books to Mary. So instead of Proverbs, it provides a choice - either the familiar (but not particularly relevant) passage from the prophet Micah about Bethlehem (Micah 5:1-4a) or Paul's famous statement about how God's redemptive election has been at work conforming the elect to the image of Christ, calling, justifying, and glorifying (Romans 8:28-30). The latter certainly seems the more appropriate option.
The Tridentine Breviary included a fitting passage from Saint Augustine's Sermon 18, which begins: the day of the blessed and ever venerable Virgin Mary so long desired is here. Let our land rejoice in the greatest exultation. Let it shine in the light of the birth of such a virgin. For she is the flower of the field, from her blossomed the precious lily of the valley. Through her birth the nature inherited from our first parents is changed. Their sin is blotted out. That unhappy curse of Eve in which it was said, "In sorrow you shall bring forth children," is, in the case of Mary, ended, for she bore the Lord in joy.
The contemporary Breviary has replaced Augustine's sermon with a discourse by Saint Andrew of Crete, which concludes: Therefore let all creation sing and dance and unite to make worthy contribution to the celebration of this day. Let there be one common festival for saints in heaven and men on earth. Let everything, mundane things and those above, join in festive celebration. Today this created world is raised to the dignity of a holy place for him who made all things. The creature is newly prepared to be a divine dwelling place for the Creator.
Both these Office readings echo Paul's theme that God's redemptive plan is at work in the created world, elevating it to a new dignity and glory in Christ. Today we celebrate an especially significant moment in that timeline of salvation, in which by a sharing in that same graced experience of being called, justified, and glorified, we too are made beneficiaries.