If you were at Mass (or one of the many Protestant congregations that use the Church's cycle of readings) this Fourth Sunday of Advent, then you heard the story of Mary's visit to Elizabeth. It is an amazingly rich story, but here I wish to highlight what it has to say to us about Mary's immaculate conception and the practice of infant baptism.
Look at Elizabeth's words to Mary: "At the moment the sound of your greeting reached my ears, the infant in my womb leaped for joy" (Luke 1:44). Let the implications of that verse sink in: The New Testament says that John the Baptist responded to grace at only six months of fetal development. John rejoiced, in utero, to be in the presence of Jesus (within the womb of Mary)! It is as the angel Gabriel had promised John's father, "He will be filled with the Holy Spirit even from his mother’s womb" (Luke 1:15).
You see, the Holy Spirit does not have to wait until a child reaches the "age of reason" to free him or her from original sin and impart supernatural life to the child's soul. This is the reason that Catholics, Orthodox, and the majority of Protestant Christians practice infant baptism. The fact that John was "filled with the Holy Spirit" and his soul able to react to Christ's presence shows us what God wants to do under the New Covenant. The only debate that you find in the early Church over infant baptism was whether, since baptism was the fulfillment of circumcision (Col. 2:11-12), infants had to wait until they were eight days old to receive it! The bishops - in perfect harmony with Luke's Gospel - said no, there was no reason to wait (Council of Carthage, 203 A.D.).
Now what, you might ask, does any of this have to do with Mary's immaculate conception? Well, this Catholic dogma states that, in lieu of Jesus's redemptive death and infinite merits, Mary was preserved, at the moment of her conception, from contracting the stain of original sin. We Catholics believe that, in baptism, both adults and infants are set free from original sin and filled with the Holy Spirit. Today's gospel reading tells us that God did this for John even before birth. The dogma of Mary's immaculate conception is absolutely consistent with all that we've seen thus far, continuing it back to the moment of conception. One may have qualms with the dogma of the Immaculate Conception, but it clearly shouldn't be over God's ability to work redemption at the moment of conception!
That's how powerful our God is to save.