Today always seems a little odd to me. In the middle or Lent we pause on March 25 to put on our white vestments and celebrate a Solemnity, the Annunciation. The intercessions for Morning Prayer begin "Today we celebrate the beginning of our salvation."
So often we think of Christmas as the day we celebrate the Incarnation, God becoming a man. But in fact today, nine months before Christmas is really the day we the incarnation took place, the great divide between heaven and earth was breached. To truly appreciate the meaning of this day we have to go back and remind ourselves of the world before the day the angel appeared.
In the Book of Genesis we are told that as God carried out the process of creation, at each step along the path he look at it and saw that it was good. When he created humanity it was elevated to "very good"—not bad but still a far cry from perfect or even excellent. Then by the misuse of our free will sin entered the world. Because we all parts of a single humanity, all humanity was wounded.
On the day the angel appeared to Mary, and she by an exercise of her free will gave her fiat, let it be done, that single humanity was once more transformed. Now God had poured himself into the created universe, divinity and humanity, perfection came into the world. Just as by the actions of one all were wounded, so back the actions of one all could be perfected.
And so it is not so strange that a week before we celebrate the culmination of Jesus's earthly mission, we pause to remember the beginning. Today, in Mary, we are reminded of what God can do through one small human being, if we will only say yes to the will of God.