John Gill Commentary 2 Chronicles 17

And Jehoshaphat his son reigned in his stead
In the stead of Asa his father:

and strengthened himself against Israel ;
the ten tribes, by fortifying his cities, building castles, raising and keeping a large standing army, as the latter part of this chapter shows, and the next verse.

And he placed forces in all the fenced cities of Judah
A considerable number of soldiers, to defend them should they be attacked:

and set garrisons in the land of Judah :
on the frontiers and borders of it, to protect it:

and in the cities of Ephraim ;
soldiers to keep garrison there:

which Asa his father had taken ;
see (2 Chronicles 15:8) .

And the Lord was with Jehoshaphat Guiding and directing, prospering and succeeding him in all things; he had, no doubt, his gracious presence in spiritual things, as well as his powerful and directing presence in things civil; the Targum is, ``the Word of the Lord was for his help;'' because he walked in the first ways of his father David; which were his best; some of his last ways not being good, as in the affair of Uriah and Bathsheba, and his numbering of the people; Jehoshaphat followed him in the one, but not in the other: or, "in the ways of David and his father, the first"; the first of them both; for the latter ways of his father Asa were not so good as his first, as the preceding chapter shows; and the Septuagint version leaves out the word "David", and so restrains it to his own father.

and sought not unto Baalim; as did Ahab king of Israel, who now reigned there; (1 Kings 15:24) (16:32) .

But sought to the Lord God of his fathers
Prayed to him, worshipped and served him:

and walked in his commandments ;
observed and kept them, moral, ceremonial, and judicial:

and not after the doings of Israel :
who worshipped the golden calves at Dan and Bethel.

Therefore the Lord stablished the kingdom in his hand
Piety is the best prop of government; the throne is best supported and established by truth, righteousness, and mercy; by the exercise of these Jehoshaphat was settled in his kingdom, and had a place in the hearts of his people:

and all Judah brought to Jehoshaphat presents ;
being well affected to him, as well as it was usual so to do at a prince's accession to the throne, see (1 Samuel 10:27)

and he had riches and honour in abundance ;
through the presents his subjects brought him, and the respect they showed him.