How is it possible to prove that the Holy Ghost was the father of Christ?
Who knows that such a being as the Holy Ghost ever existed?
How was it possible for Mary to know anything about the Holy Ghost?
How could Joseph know that he had been visited by an angel in a dream?
Could he know that the visitor was an angel? It all occurred in a dream and poor Joseph was asleep. What is the testimony of one who was asleep worth?
All the evidence we have is that somebody who wrote part of the New Testament says that the Holy Ghost was the father of Christ, and that somebody who wrote another part of the New Testament says that Joseph was the father of Christ.
Matthew and Luke give the genealogy and both show that Christ was the son of Joseph.
The "Incarnation" has to be believed without evidence. There is no way in which it can be established. It is beyond the reach and realm of reason. It defies observation and is independent of experience.
It is claimed not only that Christ was the Son of God, but that he was, and is, God.
Was he God before he was born? Was the body of Mary the dwelling place of God?