The meaning of the fact that Jesus Christ was both Man and God has proved very difficult to elucidate - despite that it is true. Clearly, the fact does not fit our normal categories of explanation.
I'm not about to solve this mystery; but one aspect has become clearer to me as a consequence of reading Owen Barfield's elusive but inspired 1958 essay The Son of God and the Son of Man. What follows is my thoughts triggered by the essay and not a summary of Barfield's conclusions.
The parentage of Christ can be considered in two ways: Jesus is a direct Son of God due to God his Heavenly Father and his Mother the Virgin Mary; Jesus is also the Son of Man by his lineage from Abraham in particular - and ultimately Adam - and this descends to him by his Mortal Father, Joseph.
Joseph is asserted to be the true King of the Jews, by his lineage from David - and Jesus inherits this 'right' from Joseph - but this is not merely a legal claim but also a divine fact. Joseph is therefore more than just the husband of Mary, but in a mystical (not genetic) sense is also and vitally Jesus's true Father.
In other words, both of Jesus's mortal parents (not just his mother) were necessary to the fullness of his nature.
I think this is most clearly seen in the genealogies at the beginning of Matthew's Gospel and Chapter 3 of Luke's Gospel. These lineages are not identical - but my point here is that they are present in the Gospels and that they culminate in Joseph.
So - we must not be misled by our modern reductionism to suppose that if Jesus was not genetically related to Joseph, then he was not related at all; thus Jesus was Joseph's true Son.
Why is this important? Well, I think it relates to the historical placement of Jesus - to the fact that he was born where and when he was; and to the fact that he was a Jew with a valid and divine claim to the Kingship of that people.
It seems to have been necessary that Jesus's lineage was on Mary's side direct in its link with God - he was the direct Son: the Son of God; and at the same time he was also, on Joseph's side an indirect and lineal, multigenerational one: the Son of Man.
This is Christ in his simultaneously Cosmic and Historical aspects - and it seems that both were and are necessary.