Matthew 1 [for reference]
Matthew’s Infancy narrative begins with a genealogy of Jesus, “the Son of David, the Son of Abraham.” [Matthew 1:1] In his Coming Christ in Advent  Father Raymond Brown writes that “I have been conducting a somewhat solitary campaign to make this Matthean genealogy a major Advent topic” and in a footnote he reminds us that “It is also assigned to the afternoon Mass on December 24—a Mass that seems not to be frequently celebrated in the U.S.A.” [p. 17] Personally I can only recall this opening text of the Gospel read once at a public Mass, and I must admit I never read the full list of Jesus’ ancestors at a public Mass as a pastor. In popular church lingo, the two genealogies of Jesus [from the Gospels of Matthew and Luke] are sometimes referred to as the “begets” or the “begats,” as in “Azor begot Zadok, Zadok begot the father of Achim, Achim begot Eliud,” etc.
The Paulist Biblical Commentary  explains that genealogies enforce the nature and importance of their subject; in the Matthean text Jesus is clearly defined as the offspring of David and Abraham. Identified with this heritage, Jesus will go on in this Gospel to fulfill the promises of Abraham and David. Abraham, of course, was esteemed as the father of the Jewish people; by the time of Jesus many of the twelve tribes had died out, and it is no accident that Matthew will describe Jesus’ selection of “the twelve” [disciples] as a statement that the integrity of Israel’s being has been restored. Likewise, the inclusion of David at the opening of the genealogy symbolizes that Jesus has fulfilled the expectations of a new David, though the Gospel bears witness to much confusion surrounding the way in which Jesus will define the promise of David. In Matthew’s later depiction of Holy Week, the crowds on Palm Sunday will salute Jesus with “Hosanna to the Son of David” but less than a week later will call for his death, agitated by the leadership of the Temple.
The Hebrew language assigns a numerical value to its letters, and the name “David” equates to the sum of fourteen. Matthew, to enhance the Davidic relationship to Jesus, divides the genealogy into three clusters of fourteen descendants. Given the times and sources available, stretching back over two millennia, the literal accuracy of Jesus’ heritage cannot be assumed, but Matthew does include some “family skeletons.” The PBC commentator observes that there are several women in the family line with “histories;” some sexual, as was the case of Bathsheba, and some with a strong Gentile connection. The inclusion of women and sexual misconduct in the family line may have been Matthew’s way of inoculating the reader for the very peculiar conclusion of the genealogy. Matthew 1:15 reads “Jacob, the father of Joseph, the husband of Mary. Of her was born Jesus, who is called the Messiah.”
Last night at Mass as I professed the Creed I was struck again by the mystery and complexity of that phrase where we bow our heads and affirm: “For us men and our salvation, He came down from heaven, and by the Holy Spirit was incarnate of the Virgin Mary and became man.” Familiarity need not breed contempt, but it can dull our minds to the literal impact of these words and how the Incarnation event was experienced by the actual persons involved. Matthew’s text gives us a window into those events. He concludes the family line [1: 16] by defining Joseph as the husband of Mary, and Mary as the mother of Jesus. But Matthew is quick to point out that there is more to this story than meets the eye, and his narrative [1;18-25] outlines this complexity in his depiction of the conception and birth of Jesus.
Matthew explains that Mary was betrothed to Joseph, but “before they lived together, she was found with child through the Holy Spirit.” [1: 18] Matthew makes it clear that Joseph is not the natural father of Mary’s child. Joseph is described as a “righteous man,” i.e., a devout observer of the Jewish Law, who is greatly distressed that his future bride is carrying a child that is not his. Matthew’s account differs significantly from Luke’s in that the Matthean account provides no indication that Mary understood her pregnancy. Joseph, faithful observer of the Law, would have been within his rights to present his apparently unfaithful future bride to Jewish authorities for censure; Deuteronomy 22: 22-23 states that the penalty for infidelity in betrothal was stoning, though by Joseph’s day the penalty was mitigated to public disgrace and banning of the unfaithful woman [and her partner].
That Joseph, given his noted fidelity to the Law, would nonetheless seek to shield his bride-to-be from public wrath is an indication of an extraordinary moral sensitivity that goes beyond the Law and would foreshadow the mercy of Jesus later in this Gospel. Continuing the narrative, a divine intervention spared both Joseph and Mary the consequences of their dilemma. Joseph is visited by an angel in a dream, who counsels him to have no fear in taking Mary as his bride and Jesus as his legal son. Joseph learns from the angel that the child has been conceived by the Holy Spirit, a son who will “save the people from their sins.” Joseph then took Mary into his home in Bethlehem, with the evangelist explaining that “he had no relations with her until she bore a son, and he [Joseph] named him Jesus.”
Matthew’s Christmas narrative illustrates the central role of Joseph in the unfolding of events, given that the genealogy has progressed from Abraham and David all the way to Joseph. Matthew’s narrative intends to reinforce the role of Jesus as Israel’s savior by emphasis upon the divine and legal fathers of Jesus. Given that Matthew’s Infancy Narrative is less well known than Luke’s, it may come as a surprise to hear that Joseph and Mary lived in Bethlehem, and that Jesus was, so to speak, born at home. How he would come to be known as “the Nazorean” is explained in Matthew 2, the next portion of the full narrative.
Matthew’s statement that Joseph had no relations with Mary until she had borne Jesus has led some to wonder if Jesus had younger brothers and sisters. The scholars I have read indicate that this is unlikely. In the first instance, Matthew’s intention is to establish that Jesus is truly the offspring of the Holy Spirit, that there is no possibility Joseph himself sired the one we worship today as “Son of God.” Second, the evidence from Scripture and secondary sources that Jesus had siblings is just about nonexistent. And finally, for Catholics, the doctrine of the Virgin Birth appears to have roots from earliest Christian days. In his classic A Marginal Jew I  Father John Meier presents third century evidence that enemies of Christianity in the third century attacked the Church by attacking Jesus’ legitimacy. The Christian writer Origen, around 250 A.D., reports hearing a tale from his enemy Celsus that Jesus fabricated the virgin birth scenario to conceal his illegitimate birth at the hands of a Roman soldier. Meier suggests that Celsus or someone created this slur by reworking the actual Gospel of Matthew, which was already widely available and read throughout the Mediterranean world. [pp. 222-229]. He adds that if enemies were attacking this doctrine so early in history, then belief in the virgin birth was already well-established in the Christian world.