Then who else ?
So the Messiah is to be a descendant of King David.
So we move on in time. David begat Solomon, who begat Rehoboam, who begat Abijah, who begat Asa, who begat Jehoshaphat, who begat Jehoram, who begat Ahaziah etc. After a lot more 'begatting' we reach King Jeconiah (also called Jehoiachin) who, apparently was so wicked that God put a curse on his offspring. This meant that no descendant of his would ever rule Israel, let alone ever be considered for the post of Messiah.
Now this is interesting from a Christian point of view because, in the New Testament, this King Jeconiah is included in one of Jesus's genealogies. A problem? We'll have to see. Now this genealogy is seen in the Book of Matthew, in the New Testament, showing how Jesus is descended, through Joseph, his father, from Abraham, Isaac and Jacob.
There is another genealogy, though, in the Book of Luke. This one traces Jesus back to the Jewish Patriarchs but this time through Mary, his mother.
But we've just proved that no Messiah could ever come from the line of Joseph, so the only way Jesus could lay claim to this position is for Joseph not to be his natural father!
In Chapter 1 of Matthew, verse 25, we read, "But he (Joseph) had no union with her (Mary) until she gave birth to a son. And he gave him the name Jesus".
So, if Joseph wasn't the father, who was?
In Luke, Chapter 1, we read that Mary was a virgin, so no-one was responsible! If we remember earlier, when we looked at Isaiah Chapter 7, "The virgin will be with child and will give birth to a son".
So the Old Testament prophecy spoke of the Messiah being born of a virgin, which is what happened in the case of Jesus. There was no earthly father, because God, Himself, was the father.