There is a song that is often played asking Mary a series of questions concerning things Jesus did. Bottom line: She knew. And while songs may sound good, in some areas accuracy does count. This is one of those times. Why? The only surprise for Mary was she was the chosen one to carry the Christ child. After that, she knew the rest. Luke makes that pretty clear.
Gabriel shows up and tells Mary some earth healing good news. For confirmation, Mary is sent to meet up with Elizabeth. When Mary meets Elizabeth, Ol’ Liz becomes filled with the Spirit and is able to know the thoughts of her child John, also filled with the Spirit and knew in the next womb over was deity. Mary sings a song demonstrating that, she knew.
A bunch of sheepherders as doing their job protecting sheep at night and suddenly the whole place lit up like a carnival show. On word of the heavenly armies (hosts) they b-line to Bethlehem, to Mary, and they see Jesus. They tell mom and dad all that was said. Next, according to the law, Jesus is presented at the temple. Simeon, also given a word from God, blesses the child and communicates what Jesus would do. Anna, a servant at the temple did the same. Jesus runs off and starts amazing the leaders of the day. The point? Mary knew and was very well informed that Jesus was the Jesus the Old Testament points to.
Jesus’ family tree goes all the way back to Adam, through Seth, through David, etc. The family tree has a history of God showing up. I’m sure Mary and Joseph were much more alert in their study of the Bible. And seeing the Old Testament is filled with stories about what Jesus would do, Mary knew.
This sort of begs the question, of what do you know about Jesus? Perhaps I’m being a bit of a curmudgeon on the song, but things like this matter. Faith is simply taking God at his word. His word predicted Jesus. His word told Mary about Jesus and what he would do. The issue is then as well as now is believing what God said. We are prone to dismissing or ignoring what God says. God did not leave us blind