As perhaps appropriate for a story about the birth of a baby, this passage is full of family relationships. It may be about the birth of the Messiah, but it is also making clear who all the players are.
(1) Jesus first, he who is born and is the Messiah.
(2) Mary, his mother, is next up.
(3) Joseph, her husband….. Not his father….
(4) Joseph is the Son of David. This is a big deal. More below.
(5) The broken relationship of husband/wife is restored to Mary and Joseph. This is protection for Mary, and the unborn baby, but also perhaps a sign or symbol of healing to come. In many places the prophets use the metaphor of husband/wife for Israel and God’s relationship and how sin has broken or twisted it, how betrayals have happened over and over as Israel strayed from God’s love and relationship (and protection?). Here a blameless girl accused of betrayal is restored to relationship. Is it so far-fetched to think of this as a sign or symbol of God restoring right relationship between Israel and God? Between Israel/God and the Whole World?
Now let’s circle back to Joseph being the Son of David. It has confused me so much that the lineage of Jesus is traced back to Adam via Joseph in those sections. This is clear a compressed version of that — we should know, because “everyone” knew, who David was (Giant-killer, King, beloved of God, etc. etc.) and that the Messiah was to spring from that lineage. So Joseph being a Son of David is crucial to the legitimacy of Jesus being the true Messiah. But he isn’t Joseph’s son by blood — the story makes it very very clear that he isn’t.
So blood doesn’t matter so much for being a true son.
Or perhaps human blood doesn’t matter so much for being a true son.
Perhaps bonds of adoption are just as strong.
Perhaps God’s love when, thanks to the blood of Jesus, He adopts us as children is that deep and true and loving and everlasting.
The story, in an almost parable-like way, makes clear every relationship, strengthens every relationship, heals and restores, and then turns the importance of “proper” relationships around: being adopted and beloved and chosen is as important (more important even?) than who your blood comes from. Love your family and … love everyone and bring them into the family?