In the Old Testament, it seems to be clear from the beginning of Israel’s existence that God had ordained them to be ruled by judges. Only after the Hebrews’ vainglorious whining and their envy of other nations, did God acquiesce by allowing them to be ruled by a king: hence Saul, Israel’s first king.
For what reason would God’s Master Plan redeem mankind–in the future– in the person of a “king”? Why would God not send the Messiah for the Jews into the world in the re-instituted capacity as Israel’s “judge”? It seems this would have been bringing His will back to the forefront for Israel and, as well as, admonishing them for wanting something that God didn’t want them to have in the first place.
During the time of the judges God was Israel’s King. When Samuel, the last of the judges, was old and dying the people asked him for a human king like the other nations had. But even though God told Samuel to grant their request, it was not His preference for them to have a merely human king (1 Sam 8:6-9). Numerous Old Testament prophecies of the Messiah confirm this (Isaiah 9:6-7, Micah 5:2) as does the angel’s promise to Mary (Luke 1:32-33).