Through which line was the Messiah promised to come, and did Israel's behavior affect it?

Les explains that God's promise to Israel is a covenant, and because it is a covenant, His mercy will never depart from them. In spite of everything Israel does in opposition to her God, He will never go back on His Word. He promised that through the line of David, coming down through Solomon and Nathan, would one day come the King, the Messiah. It had to happen regardless of what Israel did in the meantime; the covenant stands secure. Les also notes that the covenants in the Old Testament, starting with the Abrahamic in Genesis 12, then the Davidic, the Palestinian, and the covenant of the Law, could not be added to, taken away, or canceled, because they are made and will end only with God in His Heaven.