This story seems more like a literary invention than an actual historical account, since Luke draws on previously written literary traditions. The main ones that he pulled from are the “annunciation” passages of Old Testament heroes or saints, especially the birth announcements of Moses and Samuel. A careful comparison between the Old Testament stories and this fragment of the Gospel of Luke—as they do in commentaries—proves beyond the shadow of a doubt that the author is inspired more by the sacred literature of the past than the oral traditions that could have existed during Luke’s own time.
That Mary was “betrothed” or promised to Joseph must be understood in light of what we know of Jewish betrothals in those days. Marriages were usually prepared by the family. Once decided, the first step was to get the mutual consent of the spouses, in the presence of witnesses. The second was the arrival of the bride at the husband’s house. Women in Israel married very young—between the age of twelve or thirteen—which was also common in the Greco-Roman world.
Once mutual consent was given, the marriage was legal, but the whole marriage process usually took some time, roughly one year. Apparently sexual abstinence during this time was the norm, especially in Galilee where it was taken very seriously. During this period of time, the wife was prepared by her mother for her new life, the dowry was given, and the pair was kept faithful until the marriage was complete. A failure in this regard could be considered adultery. After an agreed upon time, the bride was moved to the groom’s house and the marriage was consummated.
Matthew and Luke describe this betrothal period leading up to the actual time when the marriage is consummated. Mary is the wife of Joseph, but she was still a virgin . . . at least according to the customs of Galilee.
Nothing is said in the Infancy Gospels of Matthew and Luke about whether Mary was also of the family and lineage of David. For a reader in the first century, such information was not all that important. What did matter—whether or not Joseph was Jesus’ biological father—was that Joseph adopted Jesus. A legal adoption actually had more force than being a physical descendent. One example that is very similar to Jesus’ in the Greco-Roman world is that of Augustus, an adopted child of Julius Caesar. When Caesar was declared divine (i.e., that his soul resided in another empire with the gods) after his death, Augustus was immediately appointed as divi filius (“son of god”), and, therefore, divine also. Before the composition of the Gospels, somewhere around AD 57–58, Paul of Tarsus wrote at the beginning of his letter to the Romans (1:1–3) that Jesus was the “son of God,” but had descended from David “in the flesh.”
Since it is very likely that this statement about Jesus’ Davidic lineage was taken by the apostle from a pool of traditional Judeo-Christian beliefs, it is pretty well certain that Jesus’ lineage from David was a very old belief among the followers of Jesus. For the Jewish people of that time, to be the “son of David” (i.e., the Messiah King) usually involved expectations of liberation and the salvation of Israel, even by force through the use of swords that, though wielded by man, were swung by the arm of God. This expectation included the idea that all of Israel’s enemies would be literally swept away at the arrival of the theocratic kingdom, replete with blessings—material and spiritual—in which God himself governs through the reign of the Messiah King. With that kingdom Israel would become the center of the world and the other nations would be converted in part to Yahweh as their main God, or at least they would revere him with great fear. The Prince Messiah King would reign over the house of Jacob forever, and his kingdom would never end.