This feast is something like a "little Christmas"--even in the readings, and prayers for the day. Consider this quote from Saint Anselm, which is part of the liturgy of the hours for today:"The universe rejoices with new and indefinable loveliness. Not only does it feel the unseen presence of God himself, its Creator, it sees him openly, working and making it holy. These great blessings spring from the blessed fruit of Mary’s womb."
So, even though we aren't directly celebrating the birth--or even the conception--of our Lord, yet this is a feast directly tied to it.
It got me thinking about something else we do this time of year. We anticipate Christmas for several weeks--we can't wait for it, and increasingly, we don't. As a result, Advent kind of gets swamped by ever-earlier celebrations of Christmas.
Not that I'm endorsing that; but in a sense, that's what happens when we celebrate this feast: and in a way, that's what we are celebrating. The glory of Christ is so great, that it shines out in all directions--even in time; so that the glory of the Incarnation shines backward in time, to the first instant of Mary's conception. The brilliant light of the Logos completely filled our Lady, so that no moment of her life was left in shadow.
Well, I'll have to continue these thoughts in the confessional! Merry (Little) Christmas!