Notes on the Bible, by Albert Barnes, , at sacred-texts.com
2 Chronicles 17:1
Jehoshaphat ascended the throne in the fourth year of Ahab Kg1 22:41, probably after that monarch had contracted his alliance with the royal family of Sidon, and before he was engaged in war with Syria. It was thus not unnatural that Jehoshaphat should begin his reign by strengthening himself against a possible attack on the part of his northern neighbor.
2 Chronicles 17:3
The first ways of his father David - The Septuagint and several Hebrew manuscripts omit "David," which has probably crept in from the margin, for David's "first ways" are nowhere else contrasted with his later ways. The real meaning of the writer is, that Jehoshaphat followed the example set by his father Asa in his earlier years Ch2 14:1-15; 15.
Baalim - On the plural form, see Kg1 18:18 note.
2 Chronicles 17:4
The doings of Israel - i. e. the especially idolatrous doings of the time - the introduction and establishment of the worship of Baal and the groves.
2 Chronicles 17:5
Presents - i. e. "free-will offerings," in addition to the regular taxes. See Sa1 10:27.
2 Chronicles 17:6
His heart was lifted up - This expression generally occurs in a bad sense Deu 8:14; Ch2 26:16; Psa 131:1; Pro 18:12; but here it must be taken differently. The margin "was encouraged" expresses fairly the true meaning. He first began by setting an example of faithfulness to Yahweh. He then proceeded to use his best endeavors to extirpate idolatry.
He took away the high places - Compare Ch2 20:33, and see the Ch2 15:17 note.
2 Chronicles 17:7
The princes were not sent as teachers themselves, but had the duty committed to them of seeing that the people were taught. The actual teachers were the priests and Levites of Ch2 17:8.
2 Chronicles 17:9
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.
2 Chronicles 17:11
Some of the Philistines brought Jehoshaphat presents - i. e. "some of the Philistines were among his tributaries." Compare Sa2 8:2; Kg1 4:21.
Tribute silver - Or, "much silver" - literally "silver of burthen."
The Arabians - The Arab tribes who bordered Judaea to the south and the southeast paid Jehoshaphat a fixed tribute in kind. Compare Kg2 3:4 note.
2 Chronicles 17:14
The captains of thousands; Adnah the chief - literally, "princes of thousands, Adnah the prince." The writer does not mean that Adnah (or Johohanan, Ch2 17:15) was in any way superior to the other "princes," but only that he was one of them.
Three hundred thousand - This number. and those which follow in Ch2 17:15-18, have been with good reason regarded as corrupt by most critics. For:
(1) They imply a minimum population of 1,480 to the square mile, which is more than three times greater than that of any country in the known world (circa 1880's).
(2) they produce a total just double that of the next largest estimate of the military force of Judah, the 580, 000 of Ch2 14:8.
(3) they are professedly a statement, not of the whole military force, but of the force maintained at Jerusalem (Ch2 17:13; compare Ch2 17:19).
It is probable that the original numbers have been lost, and that the loss was suppplied by a scribe, who took Ch2 14:8 as his basis.