Joseph was Jesus's legal father. According to Jewish way of thinking, the biological son of one man is considered to the the legal son of another (such as in levirate marriage, where a man dies and his brother marries with widow; the deceased's son become legal sons of the brother). This is different from adoption (The Romans had adoption; the Jews did not). Jesus was never known as Joseph's adopted son; instead, Jesus was Mary's firstborn and legally in Joseph's lineage. The fact that Joseph names Jesus (Mt. 1.25) is a clear demonstration of Jesus's legal status as his son, and thus as a legitimate heir of King David.

If Jesus was born of a virgin, how could he have have been the messiah, because his father -- the Holy Spirit -- was not a human descendent of the House of David?

Scripture says both yet both cannot be true. How can we explain the discrepancies?