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
4 Kings (2 Kings) 14:3
kg2 14:3AMAZIAH'S GOOD REIGN OVER JUDAH. (Kg2 14:1-6)
He did that which was right in the sight of the Lord, yet not like David his father--The beginning of his reign was excellent, for he acted the part of a constitutional king, according to the law of God, yet not with perfect sincerity of heart (compare Ch2 25:2). As in the case of his father Joash, the early promise was belied by the devious course he personally followed in later life (see Ch2 20:14), as well as by the public irregularities he tolerated in the kingdom.
4 Kings (2 Kings) 14:5
kg2 14:5as soon as the kingdom was confirmed in his hand--It was an act of justice no less than of filial piety to avenge the murder of his father. But it is evident that the two assassins must have possessed considerable weight and influence, as the king was obliged to retain them in his service, and durst not, for fear of their friends and supporters, institute proceedings against them until his power had been fully consolidated.
4 Kings (2 Kings) 14:6
kg2 14:6But the children of the murderers he slew not--This moderation, inspired by the Mosaic law (Deu 24:16), displays the good character of this prince; for the course thus pursued toward the families of the regicides was directly contrary to the prevailing customs of antiquity, according to which all connected with the criminals were doomed to unsparing destruction.
4 Kings (2 Kings) 14:7
kg2 14:7HE SMITES EDOM. (Kg2 14:7)
He slew of Edom in the valley of salt ten thousand--In the reign of Joram the Edomites had revolted (see Kg2 8:20). But Amaziah, determined to reduce them to their former subjection, formed a hostile expedition against them, in which he routed their army and made himself master of their capital.
the valley of salt--that part of the Ghor which comprises the salt and sandy plain to the south of the Dead Sea.
Selah--literally, "the rock"; generally thought to be Petra.
Joktheel--that is, "given" or "conquered by God." See the history of this conquest more fully detailed (Ch2 25:6-16).
4 Kings (2 Kings) 14:8
kg2 14:8JOASH DEFEATS HIM. (Kg2 14:8-16)
Amaziah sent messengers to Jehoash, the son of Jehoahaz, son of Jehu, king of Israel--This bold and haughty challenge, which was most probably stimulated by a desire of satisfaction for the outrages perpetrated by the discharged auxiliaries of Israel (Ch2 25:13) on the towns that lay in their way home, as well as by revenge for the massacre of his ancestors by Jehu (2Ki. 9:1-37) sprang, there is little doubt, from pride and self-confidence, inspired by his victory over the Edomites.
4 Kings (2 Kings) 14:9
kg2 14:9Jehoash the king of Israel sent to Amaziah--People in the East very often express their sentiments in a parabolic form, especially when they intend to convey unwelcome truths or a contemptuous sneer. This was the design of the admonitory fable related by Joash in his reply. The thistle, a low shrub, might be chosen to represent Amaziah, a petty prince; the cedar, the powerful sovereign of Israel, and the wild beast that trampled down the thistle the overwhelming army with which Israel could desolate Judah. But, perhaps, without making so minute an application, the parable may be explained generally, as describing in a striking manner the effects of pride and ambition, towering far beyond their natural sphere, and sure to fall with a sudden and ruinous crash. The moral of the fable is contained in Kg2 14:10.
4 Kings (2 Kings) 14:11
kg2 14:11But Amaziah would not hear--The sarcastic tenor of this reply incited the king of Judah the more; for, being in a state of judicial blindness and infatuation (Ch2 25:20), he was immovably determined on war. But the superior energy of Joash surprised him ere he had completed his military preparations. Pouring a large army into the territory of Judah, he encountered Amaziah in a pitched battle, routed his army, and took him prisoner. Then having marched to Jerusalem [Kg2 14:13], he not only demolished part of the city walls, but plundered the treasures of the palace and temple. Taking hostages to prevent any further molestation from Judah, he terminated the war. Without leaving a garrison in Jerusalem, he returned to his capital with all convenient speed, his presence and all his forces being required to repel the troublesome incursions of the Syrians.
4 Kings (2 Kings) 14:19
kg2 14:19HE IS SLAIN BY A CONSPIRACY. (Kg2 14:17-20)
they made a conspiracy against him in Jerusalem--Amaziah's apostasy (Ch2 25:27) was followed by a general maladministration, especially the disastrous issue of the war with Israel. The ruinous condition of Jerusalem, the plunder of the temple, and the loss of their children who were taken as hostages [Kg2 14:13-14], lost him the respect and attachment not of the grandees only, but of his subjects generally, who were in rebellion. The king fled in terror to Lachish, a frontier town of the Philistines, where, however, he was traced and murdered. His friends had his corpse brought without any pomp or ceremony, in a chariot to Jerusalem, where he was interred among his royal ancestors.
4 Kings (2 Kings) 14:21
kg2 14:21AZARIAH SUCCEEDS HIM. (Kg2 14:21-22)
all the people of Judah took Azariah--or Uzziah (Kg2 15:30; Ch2 26:1). The popular opposition had been personally directed against Amaziah as the author of their calamities, but it was not extended to his family or heir.
4 Kings (2 Kings) 14:22
kg2 14:22He built Elath--fortified that seaport. It had revolted with the rest of Edom, but was now recovered by Uzziah. His father, who did not complete the conquest of Edom, had left him that work to do.
4 Kings (2 Kings) 14:23
kg2 14:23JEROBOAM'S WICKED REIGN OVER ISRAEL. (Kg2 14:23-29)
Jeroboam, the son of Joash king of Israel--This was Jeroboam II who, on regaining the lost territory, raised the kingdom to great political power (Kg2 14:25), but adhered to the favorite religious policy of the Israelitish sovereigns (Kg2 14:24). While God granted him so great a measure of national prosperity and eminence, the reason is expressly stated (Kg2 14:26-27) to be that the purposes of the divine covenant forbade as yet the overthrow of the kingdom of the ten tribes (see Kg2 13:23).