How does the Davidic royal line reach Joseph and Mary?
The Davidic royal line begins with King David and comes down through Solomon, then through Bathsheba's two sons, Nathan and Solomon. That genealogy continues through history, nearly broken during the Babylonian captivity, until it reaches the New Testament and both Joseph and Mary, and continues until Christ was born.
Les teaches that this Davidic covenant is given in 2 Samuel chapter 7 and is surrounded by the Abrahamic covenant; every covenant God made with Israel falls within that Abrahamic covenant. He notes that David had already committed adultery with Bathsheba, she became his wife, and they had Solomon and Nathan. The royal family begins with David, comes down to Solomon, and then to Bathsheba and David's two sons, Nathan and Solomon. From there the genealogy runs all the way down through history to the New Testament and Joseph and Mary. Les also points out that once or twice it looked as though the genealogy would be broken—he calls it the wasp neck—during the Babylonian captivity, when only one man was left in the kingly line who could still have a son. It almost seemed he would not make it, and a little snip would have ended it, but God prevailed, and the genealogy continued until Christ was born.