The Annunciation to Mary in Luke (1:26-38) is sandwiched between two episodes about John the Baptist. In no way does this diminish its importance. Instead it marks the difference between the two births. The angelic annunciation gives special emphasis to the superiority of Mary’s child. Furthermore, it locates the visionary experience unquestionably in Nazareth in Galilee. That has implications for the rest of Luke’s narrative.
According to the customs of the time, Mary could have been a prepubescent child bride, engaged but not yet married, when she had this life-changing experience. (Geza Vermes gives an excellent discourse on this possibilty, pp. 78-81, in his The Nativity: History and Legend. Penguin Books, 2006). This would explain her perplexity at the words of the angel Gabriel. Mary does not understand because she does not yet share her husband’s bed and board. According to the customs of the times, while betrothed a girl still lived with her parents but was bound to her future husband for life. If she engaged in sexual activity, she could charged with adultery. After the appropriate marriage ceremony at some later date, perhaps as long as a year, she would go to live in her husband's home. Only then would a sexual union take place.
In introducing the Archangel Gabriel,Luke had tapped into much more ancient folklore of the Middle East. In the post-exilic period, Persian angelology dominated much of the development of angels in late Hebrew writing. Appearing first in Hebrew scriptures only in the early 2nd century CE Daniel (8:16 and 9:21-22 as a man) he was much more than a divine messenger. He came to give wisdom and understanding in a particularly holy situation. His power an authority increased exponentially in pseudographical literature. In Enoch 1 and 2 for instance, he sat at the left hand of God and was set over all other powers.
Gabriel’s response to Mary's anxiety about her virginity re-assured her that the Holy Spirit would play a part in her pregnancy and she would bear a holy child. To show that this would be possible, Gabriel informed her that her elderly, barren cousin Elizabeth was already six months pregnant.
The details of the annunciation reveal some unusual characteristics. Contrary to Matthew, Luke does not state unequivocally that Mary and Joseph abstained from sexual relations prior to the conception of their child. Matthew puts it circumspectly, "before they lived together." So from Luke’s perspective, the conception of Jesus could have been similar to that of John the Baptist and other accounts in the Hebrew scriptures involving normal sexual intercourse between spouses.
The angelic message extended beyond the announcement of a divinely favoured conception. The child Mary would bear was to be named Jesus, a contemporary form of Joshua, which meant “God (Yahweh) saves.” In other words, he was to have a divinely mandated redemptive mission. More than that, he would be the “Son of the Most High” (i.e. God) and heir to his ancestor David’s throne.
Brown stated that the future role of Jesus described by Gabriel had a parallel in the promise of the prophet Nathan to David in 2 Samuel 7:8-16. He called Luke’s rendering “a free interpretation” of the earlier passage. He further pointed out that the idea of a Davidic Messiah may have already existed in the Hebrew tradition. It can be found in references such as Psalms 2:7 and 89:30 as well as in Isaiah 9:5-6 and some texts discovered in the Dead Sea Scrolls.
All this illustrates why scholars generally believe that the birth narratives in both Matthew and Luke are theological rather than historical in character. More evidence of this is found in Luke 1:35 with distinctive messianic reference to Isaiah 11:1-2 and 4:2-3. It is worth noting that in the gospel narratives, the power of God’s creative Spirit comes to the child’s mother, Mary, not to the king, as in David’s case.
Most scholars believe that this interpretation, designated as “Christology,” may have existed in Christian tradition even before Paul wrote of it in Romans 1:3-4. Brown described it as “backward development,” thereby associating Mary’s conception of Jesus’ by the Holy Spirit with the narratives of Jesus’ resurrection and baptism (Luke 3:15-16, 21-22). It also helps to explain why the Nativity narratives came so late in the literature of the Apostolic Age. Theology always follows religious experience, not vice versa. Only long reflection on the true nature of that special person, Jesus of Nazareth, led the Church of the late 1st century CE to create these narratives of how he may have been born as both the Son of God and a human being.