The Annunciation story (Luke 1:26-38) is one of the most famous and familiar of all gospel readings. The scene has certianly been one of the most frequently painted and otherwise depicted in Christian art. All of which suggests the significant importance of the event.
What is this event we call the Annunciaiton? It is nothing less than the incarnation itself, the central moment in the entire span of all history, the moment when divinity assumed humanity and heaven came down to earth - a joining together the likes of which had never happened before.
Annunciation stories are somewhat standard fare in the scriptures. Just yesterday, we heard the story of the Archangel Gabriel's annunciation to Zechariah (Luke 1:5-25). Such annunciations prepare us for the coming career of the special person whose birth is being announced. It is in that Christ-centered way that we must understand Mary's question to Gabriel and Gabriel's answer - as an opportunity to explain what the Church believes about Jesus. What the resurrection revealed about Jesus to his disicples (and through them to the early Church), the Annunciation story assures us, was true from the beginning and was revealed to Mary at the moment of Christ's conception in her virginal womb.
The purpose of Mary's question and Gabriel's answer was to say something about Jesus. When we get to Mary's answer, however, we're being told something significant about Mary - and, through Mary, about what it must mean for one to be a true disicple. Mary's answer indicates that she heard and accepted Christ's coming, becoming the first of those her Son would later praise who hear the word of God and observe it (Luke 11:28). In saying that, Jesus would broaden the meaning of Mary's motherhood, so that it became something in which we can all come to share. In showing the Holy Spirit at work in such a unique and special way in Mary, the Annunciation prepares us for the Holy Spirit's work in us in the Church - something we start to see happening already in the very next episode, tomorrow's story of the Visitation of Mary to Elizabeth (Luke 1:39-45).