Here is what C.S. Lewis had to say about having faith in the virgin birth of Jesus:
“The grounds for belief and disbelief are the same today as they were two thousand…years ago. If Joseph had lacked faith to trust God or humility to perceive the holiness of his spouse, he could have disbelieved in the miraculous origin of her Son as easily as any modern man; and any modern man who believes in God can accept the miracle as easily as Joseph did.”
“Therefore the Lord himself will give you a sign: The virgin will conceive and give birth to a son, and will call him Immanuel.”—Isaiah 7:14