(Matthew 1:18-25) Most of us know this story. Mary and Joseph were going to get married, but they were not married yet. She is pregnant but Joseph knows he is not the father. However, the narrative makes clear that the pregnancy is of God. The explanation is for our benefit.
Joseph is righteous. For Matthew that means both he obeyed the Law and that he was moral and upright. His decision to divorce her is based on the grave nature of the situation. He assumes she has commited adultery. Yet he wants to do it "quietly." He is not trying to get revenge or publicly humilate her (even though he thinks she has done this to him). Like his namesake in Genesis, it is in the world of dreams that God speaks to Joseph. A messenger (Greek angelos = messenger) explains to Joseph that this is God's activity and that he has no need to feat taking Mary as his wife.
What we have laid out before us is pretty sparse. I am always aware of how little we are told. We do not know the length of time that all of this took place. We are not given details of the inner experience of Joseph or Mary: their feelings, worries, expectations, etc. Nor do we hear how friends and family react. The story is not told for us to have such insights or information. (In a sense, their privacy is respected.)
What we do know is central. God is at work here. The pregnancy is an act of God. This is emphasized by connecting the event to a verse from Isaiah 7:14. In the Isaiah story the prophet Isaiah tells the king, Ahaz, to ask for a sign. The king refuses and Isaiah blasts him for his insolence. Then he makes a prophecy about a child being born. This child, Isaiah says, will be weaned around the time Israel is delivered from its current threat. Isaiah is not prediciting that a virgin (in Hebrew the word means young woman) will have a baby and that the baby will be a Messiah. However, Matthew connects the deliverance of Israel seven centuries prior to the deliverance to be given by Jesus. Fulfillment in the sense of FULLNESS is probably the best understanding. God is at work. Jesus will save His people from their sins. Big deals begin in small ways. Man-Kings start out as helpless infants. Insignifcant people, living holy and faithful lives, may find those lives turned upside down by God. To save the world God may upset your own little household. But in it all, the Holy Spirit is the author and God's messengers do show up (even if it is a dream). The many struggles of Joseph and Mary are something to reflect on. Being Jesus' mom and dad was a great blessing. When you serve God, great blessings are often a challenge (cross shaped). Matthew's Christmas story may be sweet to us because of warm feelings and carols we have sung. But if you look into the text more deeply it appears it could be full of real life challenges and struggles. But no matter how tough it is, Emmauel--God is with us. Even if he is present in the flesh of a baby!