Hello dantech,
What I actually said was .....
This genealogy from both of Jesus' parents was proved that he was indeed a "son of David". Which was part of the credentials needed to prove his claim to be Messiah. It had little to do with inheritance.
The prophesy in Isaiah 9:6, 7 (CJB) says....
" For a child is born to us,
a son is given to us;
dominion will rest on his shoulders,
and he will be given the name
Pele-Yoetz El Gibbor
Avi-Ad Sar-Shalom
[Wonder of a Counselor, Mighty God,
Father of Eternity, Prince of Peace],
6 (7) in order to extend the dominion
and perpetuate the peace
of the throne and kingdom of David,
to secure it and sustain it
through justice and righteousness
henceforth and forever.
The zeal of Adonai-Tzvaot
will accomplish this."
It was the opinion of those who knew the family that Joseph was Jesus' legal father as well as his siblings, but he was the firstborn of the family.
"Adonai has sworn it,
and he will never retract
You are a cohen (priest) forever,
to be compared with Malki-Tzedek. (Psalm 110:4 CJB)
Since the Messiah was prophesied to be both a king and a priest, according to the manner of "Malki-Tzedek", (Mel·chiz′e·dek, a king/priest whose genealogy is not revealed) both the prophesy in Isaiah and Psalm 110 indicate that it was only by God's declaration that this was so. The kingly tribe and the priestly tribe were separate. Messiah was to be a "son of David" (kingly tribe) as his genealogy proved but he was also to be a priest.