The LORD was with Jehoshaphat because he followed the example of his father's early years and did not worship the images of Baal.
References for 2 Chronicles 17:3
He sought his father's God and obeyed his commands instead of following the practices of the kingdom of Israel.
So the LORD established Jehoshaphat's control over the kingdom of Judah. All the people of Judah brought gifts to Jehoshaphat, so he became very wealthy and highly esteemed.
He was committed to the ways of the LORD. He knocked down the pagan shrines and destroyed the Asherah poles.
In the third year of his reign, Jehoshaphat sent out his officials to teach in all the towns of Judah. These officials included Ben-hail, Obadiah, Zechariah, Nethanel, and Micaiah.
He sent Levites along with them, including Shemaiah, Nethaniah, Zebadiah, Asahel, Shemiramoth, Jehonathan, Adonijah, Tobijah, and Tob-adonijah. He also sent out the priests, Elishama and Jehoram.
They took copies of the Book of the Law of the LORD and traveled around through all the towns of Judah, teaching the people.