The biblical women who have these surprise children give birth to significant figures who carry forward God's covenant in important ways. Sarah (Isaac), Rebekah (Jacob), Rachel (Joseph), Hannah (Samuel) all fit this pattern.
When the prophet Isaiah confronts Judah's King Ahaz, he challenges his approach to a difficult poilitical situation involving Judah's northern neighbors, Israel and Aram. He demands that the king seek a sign from God who is ready to provide for him. The king demurs, suddenly finding (false) piety. Aggravated by the king's inaction (and ineptitude), Isaiah declares that an unnamed pregnant woman will bear a son who will be called Emmanuel.
In other words, God is providing a sign, even though the king hasn't brought himself to ask for one. The sign makes clear that God will be with God's people as they remain faithful. The threats that have the king cowering will be negated. However, failure in a faithful response will bring even worse, the brunt of the Assyrian army.
In Matthew's account of the nativity, the focus is on Joseph, not Mary. Give Joseph a break. He isn't running away, but trying to do the best thing. However, a nocturnal vision with an angelic visitor persuades him to reconsider. Frankly, he doesn't get any new information beyond what Mary has likely shared with him. But he decides to act faithfully with the angel's affirmation.
Like I said, this child comes to shake things up. Mary makes that very clear as we heard last week. Both Joseph and Mary certainly have their lives upended by this surprise child.
Even with our best Advent preparations, are we prepared for Emmanuel - "God with us" - coming to shake up our lives?
Explore the whole story and its nuances in the sermon video below, noting the downloads available below the video panel.