Through what lineage did God promise the Messiah would come?
God promised the Messiah would come through the line of David, specifically coming down through Solomon and Nathan. That Davidic covenant stood secure, so the King and Messiah would one day come regardless of what Israel did in the meantime.
Les teaches that God's mercy will never depart from Israel because it is a covenant, and God will never go back on His Word. He explains that God promised the King, the Messiah, would come through the line of David, coming down through Solomon and Nathan. That had to happen regardless of what Israel did in the meantime, because the covenant stands secure. Les also notes the Old Testament covenants—Abrahamic, Davidic, Palestinian, and the covenant of the Law—could not be added to, taken away, or canceled, since they end only with God in His Heaven. In Galatians 3:16, Paul says the promises were made to Abraham and his seed, singular, who is Christ.