2-chronicles 17:9

Had the book of the law of the Lord with them - This was their text book: it was the book of God; they taught it as such, and as such the people received it. Its laws were God's laws, and the people felt their obligation, and their consciences were bound. Thus they were obedient to the laws of the land, on the principle of religion. In this they were encouraged and confirmed by the example of all, both in Church and state. The princes were not only pious, but were teachers of piety; the Levites showed them the worth and excellence of their ritual institutions; and the priests showed them the moral use they were to make of the whole: and thus the people became obedient to God as well as to the king, and kept all the civil ordinances, not merely for the sake of a good king, but for the sake of a good and gracious God. By these means the nation enjoyed peace and prosperity; and all insurrections, seditions, and popular commotions, were prevented. The surrounding nations, perceiving this, saw that there was no hope of subduing such a people, so they made no war with Jehoshaphat, 2 Chronicles 17:10. And they took care not to provoke such a people to fall on them; therefore, it is said, The fear of the Lord fell on all the kingdoms and lands that were round about Judah. Such an itinerant ministry established in these kingdoms for upwards of fourscore years, teaching the pure, unadulterated doctrines of the Gospel, with the propriety and necessity of obedience to the laws, has been the principal means, in the hand of God, of preserving these lands from those convulsions and revolutions that have ruined and nearly dissolved the European continent. The itinerant ministry, to which this refers, is that which was established in these lands by the late truly reverend, highly learned and cultivated, deeply pious and loyal John Wesley, A.M., formerly a fellow of Lincoln College, Oxford, whose followers are known by the name of Methodists; a people who are an honor to their country, and a blessing to the government under which they live.

There is no reasonable doubt that this "book of the law" was the Pentateuch - nearly, if not quite, in the shape in which we now have it. Copies of the whole Law were, no doubt, scarce; and therefore Jehoshaphat's commission took care to carry a copy with them.

17:9 And they taught, &c. - And these itinerant judges and itinerant preachers together, Mr. Henry observes were instrumental to diffuse a blessed light throughout the cities of Judah.