Joseph, the husband of Mary, was not king at the time of Jesus' birth because he was not a member of the reigning Herodian dynasty. Here's a breakdown:
* The Davidic Lineage: Joseph was a descendant of King David, which was significant because Jewish prophecies foretold that the Messiah would come from David's line. However, lineage alone was not enough to claim kingship at that time.
* Roman Rule and the Herodians: Judea was under Roman rule during the time of Jesus' birth. The Romans had installed Herod the Great as King of Judea. Herod was not of Jewish descent, although he tried to integrate into Jewish society. After Herod's death, the kingdom was divided among his sons, who ruled as tetrarchs, still under Roman authority. None of them were from the Davidic line.
* Political Reality: The political landscape of Judea was complex. Even if Joseph had claimed kingship based on his Davidic lineage, he would have faced immediate opposition from the Herodian rulers and the Roman authorities. A direct claim to kingship would have been seen as an act of rebellion against Rome.
In essence, while Joseph's lineage connected Jesus to the prophesied line of David, the political reality of Roman occupation and the Herodian dynasty meant that the Jewish kingship was not accessible through lineage alone.