A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
2 Chronicles 25:1
ch2 25:1AMAZIAH BEGINS TO REIGN WELL. (Ch2 25:1-4)
Amaziah was twenty and five years old, &c.--(See Kg2 14:1-6).
2 Chronicles 25:5
ch2 25:5HAVING HIRED AN ARMY OF ISRAELITES AGAINST THE EDOMITES, AT THE WORD OF A PROPHET HE LOSES A HUNDRED TALENTS AND DISMISSES THEM. (Ch2 25:5-10)
Amaziah . . . made captains, &c.--As all who were capable of bearing arms were liable to serve, it was quite natural in making up the muster-roll to class them according to their respective families and to appoint the officers of each corps from the same quarter; so that all the soldiers who formed a regiment were brothers, relatives, friends. Thus the Hebrew troops were closely linked together, and had strong inducements to keep steady in their ranks.
found them three hundred thousand choice men--This was only a fourth part of Jehoshaphat's army (Ch2 17:14-19), showing how sadly the kingdom of Judah had, in the space of eighty-two years, been reduced in population by foreign wars, no less than by internal corruptions. But the full amount of Amaziah's troops may not be here stated.
2 Chronicles 25:6
ch2 25:6He hired also an hundred thousand mighty men of valour . . . for an hundred talents of silver--This sum was paid into the treasury of Jehoahaz--not given as bounty to the mercenaries who were obliged to serve at the sovereign's call; their remuneration consisting only in the booty they might obtain. It was about Â£50,000 sterling, being 10s. per man, including officers--a very paltry pay, compared with the bounty given for a soldier in this country. But it must be remembered that in ancient times campaigns were short and the hazards of the service comparatively small.
2 Chronicles 25:7
ch2 25:7there came a man of God--sent to dissuade Amaziah from the course he was following, on the ground that "the Lord is not with Israel." This statement was perfectly intelligible to the king. But the historian, writing long after, thought it might require explanation, and therefore added the comment, "with all the children of Ephraim." Idolatry had long been the prevailing religion in that kingdom, and Ephraim its headquarters. As to the other part of the prophet's advice (Ch2 25:8), considerable obscurity hangs over it, as the text stands; and hence some able critics have suggested the insertion of "not" in the middle clause, so that the verse will be thus: "But if thou wilt go [alone], do, be strong for the battle; God shall not make thee fall before the enemy."
2 Chronicles 25:10
ch2 25:10separated them . . . the army . . . out of Ephraim . . . their anger was greatly kindled against Judah--Amaziah, who knew his position as the Lord's viceroy, complied with the prophet's counsel, and, consenting to forfeit the purchase money of the Israelitish soldiers, discharged them. Exasperated at this treatment, they resolved to indemnify themselves for the loss of their expected booty, and so on their return home they plundered all the towns in their way, committing great havoc both of life and property without any stoppage, as the king of Judah and his army had set out on their expedition (Kg2 14:7).
2 Chronicles 25:11
ch2 25:11valley of salt--This ravine lies to the south of the Dead Sea. The arms of Amaziah, in reward for his obedience to the divine will, were crowned with victory--ten thousand of the Edomites were slain on the field, and as many taken prisoners, who were put to death by precipitation "from the top of the rock" [Ch2 25:12]. This rock might be situated in the neighborhood of the battlefield, but more probably it formed one of the high craggy cliffs of Selah (Petra), the capital of the Edomites, whither Amaziah marched directly from the Valley of Salt, and which he captured (Kg2 14:7). The savage cruelty dealt out to them was either in retaliation for similar barbarities inflicted on the Hebrews, or to strike terror into so rebellious a people for the future. The mode of execution, by dashing against stones (Psa 137:9), was common among many ancient nations.
2 Chronicles 25:14
ch2 25:14Amaziah . . . brought the gods of the children of Seir--The Edomites worshipped the sun under different forms and with various rites. But burning incense upon altars was a principal act of worship, and this was the very thing Amaziah is described as having with strange infatuation performed. Whether he had been captivated with the beauty of the images, or hoped by honoring the gods to disarm their spite at him for his conquest and harsh treatment of their votaries, his conduct in establishing these objects of religious homage in Jerusalem was foolish, ignorant, and highly offensive to God, who commissioned a prophet to rebuke him for his apostasy, and threaten him with the calamity that soon after befell him.
2 Chronicles 25:16
ch2 25:16as he talked with him, &c.--Those who were invested with the prophetic character were entitled to counsel kings. Amaziah, had he not been offended by unwelcome truths, would have admitted the claim of this prophet, who was probably the same that had given him counsel previous to the war with Edom. But victory had elated and blinded him.
2 Chronicles 25:17
ch2 25:17HE PROVOKES JOASH TO HIS OVERTHROW. (Ch2 25:17)
Then Amaziah . . . sent to Joash . . . Come, let us see one another in the face--(See on Kg2 14:8-20).