I love the way the Liturgy plays with time, as evidenced by the "birthdays" in the Church year. Today is one of them: the three "big" birthdays that the Liturgy marks with a special celebration. Oddly enough, today, Mary's birthday, is only a "Feast." (The other two birthdays get the highest possible liturgical "rank": solemnity.) But then, the feast of the Immaculate Conception (which we celebrated exactly nine months ago) is a solemnity. As is the feast of the Annunciation of the Lord (the virginal conception of Jesus in Mary's womb), nine months before Christmas Day. That leaves one more birthday in the liturgical year: the Solemnity of the Birth of John the Baptist (whose conception, being fairly ordinary--Elizabeth's age notwithstanding--gets treated more discreetly). In their own way, Mary and John went "before the Lord to prepare his way." Everything about them pointed to Jesus. Even the Solemnity of the Birth of John the Baptist (June 24) points to Jesus, since it comes at the time of the summer solstice, as the sun begins to decrease, six months before the vigil of Christmas near the time of the winter solstice, when the sun begins again to increase*.
These three liturgical birthdays have a special importance, because they highlight God acting in history, in real time. (That's another good reason for hearing the geneaology of Jesus in today's Gospel.) If God didn't act in history, we could really wonder if faith had anything to say to us in real life. Mary, John and Jesus are solidly anchored in human history, and the liturgy helps us keep them there!
*"He must increase, I must decrease," John would say at the height of his ministry.