A voice of one calling:
In the wilderness, prepare
the way for the Lord;
make straight in the desert
a highway for our God.
These words from Isaiah are referenced by Mark to open his account of the coming of Christ (Mark 1:3). The story Mark wants to tell is not like the later advent stories in Matthew and Luke about the birth of Jesus or like John’s profound elucidation of the significance of that event: “The Word became flesh and dwelt among us (John 1).” For Mark, the advent of Christ was not his birth but the launch of his ministry. Perhaps that emphasis is particularly appropriate for the first written gospel, because it was not in his mother's miraculous pregnancy but in his own ministry that Jesus was first recognized by his followers as the Christ.
Indeed, who would have known that there was anything unique about Jesus or his birth? Jesus apparently knew (Luke 2:49). Mary and Joseph would have known as would Zechariah and Elizabeth. Luke tells of shepherds down in the region of Judea who knew (Luke 2), and Matthew tells of some mysterious magi from a far-off eastern country who knew (Matthew 2). But there was no indication of widespread, general knowledge of the miraculous circumstances of Jesus’ birth. It certainly appears that there was no such knowledge in the region of Galilee where Jesus grew up and where all his disciples came from. To all that world, he was nothing other than the son of Joseph, the carpenter (Matthew 13:55; John 6:42).
When Martha (John 11:27) and Peter (Matthew 16:16) first acknowledged that Jesus was the Christ, they made no reference to the virgin birth as a reason for their faith. And they would not yet have known of his death or his resurrection. What they knew of Jesus was what they experienced as they followed him, hearing what he said and seeing what he did. Through this relationship, the Father revealed His Christ (Matthew 16:17).
We must note that when John the Baptist sent messengers to Jesus asking, “Are you the one we have been waiting for, or should we look for another,” Jesus did not say, “Remind cousin John that I was born of a virgin. That should convince him.” Instead, he said, “Go and tell John what you hear and see...(Matthew 11:1-6).”
The Messiah would not be recognized by his match-up with Old Testament prophecy, nor would he be known by magical acts such as turning his staff into a snake, leaping off a tall building to be caught by angels, or walking across a swimming pool, but by words (John 6:68) and by deeds (John 11:45, et al).
That Jesus was born of the virgin Mary became an affirmation of the creeds developed later by the church. However, it was not a detail that played any part in revealing Jesus as the Christ when he walked and talked on this earth, nor is assent to it as historical fact essential or adequate for genuine discipleship today.