To teach in the cities of Judah - "To teach the fear of the Lord in the cities of Judah." - Targum.

In these verses we find a remarkable account of an itinerant ministry established by Jehoshaphat; and in this work he employed three classes of men:

1. The princes.

2. The Levites.

3. The priests.

We may presume that the princes instructed the people in the nature of the civil law and constitution of the kingdom; the Levites instructed them in every thing that appertained to the temple service, and ritual law; and the priests instructed them in the nature and design of the religion they professed. Thus the nation became thoroughly instructed in their duty to God, to the king, and to each other. They became, therefore, as one man; and against a people thus united, on such principles, no enemy could be successful.

priests

Ezra 7:1-6 Now after these things, in the reign of Artaxerxes king of Persia, Ezra the son of Seraiah, the son of Azariah, the son of Hilkiah...

Malachi 2:7 For the priest's lips should keep knowledge, and they should seek the law at his mouth: for he is the messenger of the LORD of hosts.

Chronicles
The comparative indifference with which Chronicles is regarded in modern times by all but professional scholars seems to have been shared by the ancient Jewish church. Though written by the same hand as wrote Ezra-Nehemiah, and forming, together with these books, a continuous history of Judah, it is placed after them in the Hebrew Bible, of which it forms the concluding book; and this no doubt points to the fact that it attained canonical distinction later than they. Nor is this unnatural. The book …
John Edgar McFadyen—Introduction to the Old Testament