Herod was "troubled"–not about the star, but because a "king of the Jews" had been born. He understood that this meant the Messiah. The Messiah was a leader of the Jewish people, and had been spoken of in Old Testament prophecies. So he asked his helpers where the Messiah would be born. They replied that the Messiah would be born in Bethlehem, the place where King David was born, remembering what the prophet Micah had said. The king told this to the magi.