Note that Amariah, the chief priest, will be over you in all that pertains to the LORD, and Zebadiah son of Ishmael, the ruler of the house of Judah, in all that pertains to the king. And the Levites will serve as officers before you. Act resolutely; may the LORD be with the upright!”
Jehoshaphat, having done what he could to make his people good, is here providing, if possible, to keep them so by the influence of a settled magistracy. He had sent preachers among them, to instruct them (Ch2 17:7-9), and that provision did well; but now he saw it further requisite to send judges among them, to see the laws put in execution, and to be a terror to evil-doers.
Commenting on 2 Chronicles 19:5-11
And, behold, Amariah the chief priest [is] over you in all matters of the LORD; and Zebadiah the son of Ishmael, the ruler of the house of Judah, for all the king's matters: also the Levites [shall be] officers before you. Deal courageously, and the LORD shall be with the good. (h) Shall be chief overseer of the public affairs of the realm.
Behold, Amariah - Here was a two-fold jurisdiction, ecclesiastical and civil: in the ecclesiastical court, Amariah the high-priest was supreme judge, in the civil court, Zebadiah was supreme. To assist both the Levites were a sort of counsellors. Without good and wholesome laws, no nation can be prosperous: and vain are the best laws if they be not judiciously and conscientiously administered.