David turned from lamenting about his enemies to prophesying the coming of the Messiah. Hundreds of years later Jesus, the Messiah did take His seat of honor on the throne of David at the right hand of God. The rod of Christ’s authority came from God. Kings did not become priests. Jesus of the tribe of Judah, instead of the priestly tribe of Levi became both King and Priest eternally after the order of Melchizedek, King of Salem. The Messiah did not depend upon human lineage to the priesthood just as Melchizedek had no earthly lineage to the priesthood. After all of the trials and tribulations of an earthly life, the King, Jesus will be/was triumphant.