Okay, so the Immaculate Conception is a good excuse for a feast, but a solemnity? A holy day of obligation?
It's understandable that, when a dogma is solemnly pronounced, the pope might create a holy day of obligation to emphasize it. But is the Immaculate Conception really so central to the Catholic faith that we still need to make everyone come to Mass to hear it mentioned? Is it (and, for that matter, the Assumption) really up there with Christmas and the Annunciation and the Ascension? From a purely pastoral point of view, might it not be better to create a Solemnity of Jesus Wasn't Just a Wise Teacher Like the Buddha or Ghandi?
The hyperdulia, or extreme honor, Catholics show to Mary is a positive virtue. St. Thomas places it among the virtues connected with justice, and writes:
Honor [dulia] denotes a witnessing to a person's excellence... [A]s regards men, one cannot bear witness, save by means of signs, either by words, as when one proclaims another's excellence by word of mouth, or by deeds, for instance by bowing, saluting, and so forth, or by external things, as by offering gifts, erecting statues, and the like. Accordingly honor consists of signs, external and corporal.
To honor the Blessed Virgin, then, is to give due witness to her unique excellence. We might say that making today's solemnity a day of obligation is not just a good idea from a didactic perspective, but an act of justice.
But of course it is much more. It draws us closer to Mary, and therefore to Jesus. It nurtures a Marian habit in us, which encourages us to turn to Mary as our mother -- and as our teacher, as the Pope reminds us with his memorable phrase "the contemplation of Christ at the school of Mary."
This feast in particular also calls to mind a fact of our own conceptions we might prefer to overlook. "In guilt I was born, a sinner was I conceived." There's not much we can do about that, but we can take heart from the example of Mary, who accepted God's troubling gift of grace, triumphed over both original and actual sin through the sacrifice of her Son, and is now glorified in Heaven giving glory to God.
Only through God's grace can we overcome our origin; from the moment of conception, we've been unreliable in choosing the good and avoiding evil. Mary was perfectly reliable, but not because of her own efforts. The graces she received were unique, but the Source of her graces is just as eager to give us each our own unique, if less exalted, graces.
And finally, the Immaculate Conception is all about grace, and grace is all about giving what doesn't need to be given. If we truly understand that we have no more claim today on any gift of God, including our continued existence, than we had claim, at the moment of our conception, to be kept preserved from all stain of original sin, then we might begin to appreciate the thanksgiving we truly owe God for everything; most of all for what he gave us, which didn't need to be given, through Mary on that day we will celebrate this Christmas.