"The Annunciation" by Caravaggio
The first place is Matthew 1:20 where we read, "But after he [Joseph] had considered this, an angel of the Lord appeared to him in a dream and said, 'Joseph son of David, do not be afraid to take Mary home as your wife, because what is conceived in her is from the Holy Spirit."
The second place is in Luke 1:35 where we read about an angel saying something similar to Mary: "The Holy Spirit will come upon you, and the power of the Most High will overshadow you. So the holy one to be born will be called the Son of God."
Some people reject the Virgin Birth arguing that, since the story is told in only these two places in Matthew and Luke, we can very well do without it.
In one sense this may have a bit of truth to it. N. T. Wright (in his book with Marcus Borg, The Meaning of Jesus) says,
Jesus' birth usually gets far more attention than its role in the New Testament warrants. Christmas looms large in our culture, outshining even Easter in the popular mind. Yet without Matthew 1-2 and Luke 1-2 we would know nothing about it. Paul's gospel includes Jesus' Davidic descent, but apart from that could exist without mention of his birth. One can be justified by faith with no knowledge of it. Likewise, John's wonderful theological edifice has no need of it: God's glory is revealed, not in the manger, but on the cross.However, just because the Virgin Birth is not mentioned anywhere else in the New Testament, that does not mean it did not happen. Wright goes on to say that there are natural, probing questions that the historian wants to ask.
As with most ancient history, of course, we cannot verify independently what is reported in only one source. If that gives grounds for ruling it out, however, most of ancient history goes with it. Let us by all means be suspicious, but let us not be paranoid. Just because I've had a nightmare, that doesn't mean there aren't burglars in the house. The fact that Matthew says something fulfilled scripture doesn't mean it didn't happen.The specifics of how this miracle was accomplished are not given in Scripture. We are not told exactly how Jesus was conceived in the womb of the Virgin Mary; we are simply told that it was by the Holy Spirit and no male was involved.
Some reject the Virgin Birth because they believe it is imported into the New Testament from other ancient myths. However, the Virgin Birth of Jesus is not a case of God taking human form and lying with a woman as in the myth of Zeus and Alcmena. There is no hint of this at all. We are simply told that the Holy Spirit "came upon" Mary and the power of the Most High "overshadowed" her. Once again, Wright offers helpful comment:
Of course, legends surround the birth and childhood of many figures who afterward become important. As historians, we have no reason to say that this did not happen in the case of Jesus and some reasons to say that it did. But by comparison with other legends about other figures, Matthew and Luke look after all quite restrained.So, how the Virgin Birth was accomplished is shrouded in mystery. However, as John Calvin one said, where God chooses to keep things a mystery we may bow in wonder and awe.