In Scripture, Isaiah prophecies that God will send his Promised One into the world. And the birth of this Promised One will be a miracle.
Biblical prophecy draws a map concerning the Messiah. We have a map, so when he comes, people will be able to recognize him. One of the more unusual prophecies, the Messiah's mother will be a virgin. In other words, in a world where babies are born all the time, and, in order for a baby to be conceived, there must be a mother and a father … in the case of the Messiah, there will only be a mother.
Or, if you take a step back, the father will be God.
Muslims have a hard time with this. They say that God would never have had physical relations with Mary. I highly doubt that there has been any Christian ever, who believed that was the way it worked. God, who made elephants, whales, and robins, as well as men and woman, is perfectly capable of creating one seed, and one egg, putting them together, and then teleporting the resulting zygote into Mary's body.
What amazes me more than the biological miracle is the sociological, and psychological interactions of the people involved.
Here is a normal teenager, hanging out in her room — maybe listening to her favorite tunes on Spotify, while looking at pictures her friends posted on Instagram — when an angel appears in the room. Imagine the range of emotions racing through Mary: amazement, curiosity, fear, confusion. Or maybe none of those. Maybe peace, calm, and wonder.
The angel tells Mary that God has a job for her. She will be the mother of the Promised One. And the angel gives a summary of what this baby will accomplish. Mary points out that with every other baby in the world, a father is involved. The angel says God has that covered. And Mary believes the angel. There is no confusion, denial, grief, or anger. There is acceptance.
This is an unusual woman. God has just turned her world upside down, and inside out, and she does not flinch, she does not blink.
Mary is pregnant with Jesus by the Holy Spirit. And she is beginning to show signs of being pregnant. And, like Mary, like everyone else in the world, Joseph knows that baby making involves one man, and one woman. In that culture, a betrothed couple were considered to be married, just not living together yet. So, logically, Mary had been unfaithful.
That culture took being unfaithful very seriously. Women found to be unfaithful were often stoned. That is, everyone in the village threw rocks at the woman, until she was dead.
So, Joseph, facing what looks like his wife being unfaithful, and all the emotions that involves (sorrow, embarrassment, inadequacy, anger, confusion) and knowing what the rules and penalties of his culture were, has an amazing response. He should be calling for Mary's stoning. Instead, he is seeking a way to end the marriage, but in a way where Mary avoids the anger of the community. He gets sucker-punched by his wife, but seeks a way to give mercy.
Of course, the angel comes back, and appears to Joseph. "Hey, Joseph! You know that crazy story Mary told about the Holy Spirit, and the baby being the Messiah? We, guess what, it's true!"
And Joseph believes. God has just turned his world upside down, and inside out, and he does not flinch, he does not blink. He marries Mary.
We have two people, who, in terms the world understands, were not much. But, in terms God understands, they were two amazing, rare, and unusual people.