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) 21:1
kg2 21:1MANASSEH'S WICKED REIGN, AND GREAT IDOLATRY. (2Ki. 21:1-18)
Manasseh was twelve years old when he began to reign--He must have been born three years after his father's recovery; and his minority, spent under the influence of guardians who were hostile to the religious principles and reforming policy of his father, may account in part for the anti-theocratic principles of his reign. The work of religious reformation which Hezekiah had zealously carried on was but partially accomplished. There was little appearance of its influence on the heart and manners of the people at large. On the contrary, the true fear of God had vanished from the mass of the people; corruption and vice increased, and were openly practised (Isa 28:7, &c.) by the degenerate leaders, who, having got the young prince Manasseh into their power, directed his education, trained him up in their views, and seduced him into the open patronage of idolatry. Hence, when he became sovereign, he introduced the worship of idols, the restoration of high places, and the erection of altars or pillars to Baal, and the placing, in the temple of God itself, a graven image of Asherah, the sacred or symbolic tree, which represented "all the host of heaven." This was not idolatry, but pure star-worship, of Chaldaic and Assyrian origin [KEIL]. The sun, as among the Persians, had chariots and horses consecrated to it (Kg2 23:11); and incense was offered to the stars on the housetops (Kg2 23:12; Ch2 33:5; Jer 19:13; Zep 1:5), and in the temple area with the face turned toward the sunrise (Eze 8:16).
4 Kings (2 Kings) 21:5
kg2 21:5the two courts of the house of the Lord--the court of the priests, and the large court of the people.
4 Kings (2 Kings) 21:6
kg2 21:6made his son pass through the fire--(See on Kg2 16:3).
observed times--from an observation of the clouds.
used enchantments--jugglery and spells.
dealt with familiar spirits--Septuagint, "ventriloquists," who pretended to ask counsel of a familiar spirit and gave the response received from him to others.
and wizards--wise or knowing ones, who pretended to reveal secrets, to recover things lost and hidden treasure, and to interpret dreams. A great influx of these impostors had, at various times, poured from Chaldea into the land of Israel to pursue their gainful occupations, especially during the reigns of the latter kings; and Manasseh was not only their liberal patron, but zealous to appear himself an adept in the arts. He raised them to be an influential class at his court, as they were in that of Assyria and Babylon, where nothing was done till they had ascertained the lucky hour and were promised a happy issue.
4 Kings (2 Kings) 21:7
kg2 21:7And he set a graven image--The placing of the Asherah within the precincts of the temple, which was dedicated to the worship of the true God, is dwelt upon as the most aggravated outrage of the royal idolater.
4 Kings (2 Kings) 21:8
kg2 21:8Neither will I make the feet of Israel move . . . out of the land which I gave their fathers--alluding to the promise (Sa2 7:10).
only if they will observe, &c.--This condition was expressed from the first plantation of Israel in Canaan. But that people not only did not keep it, but through the pernicious influence of Manasseh, were seduced into greater excesses of idolatrous corruption than even the original Canaanites.
4 Kings (2 Kings) 21:10
kg2 21:10And the Lord spake by his servants the prophets--These were Hosea, Joel, Nahum, Habakkuk, and Isaiah. Their counsels, admonitions, and prophetic warnings, were put on record in the national chronicles (Ch2 33:18) and now form part of the sacred canon.
4 Kings (2 Kings) 21:12
kg2 21:12whosoever heareth of it, both his ears shall tingle--a strong metaphorical form of announcing an extraordinary and appalling event (see Sa1 3:11; Jer 19:3; also Hab 1:5).
4 Kings (2 Kings) 21:13
kg2 21:13the line of Samaria, and the plummet of the house of Ahab--Captives doomed to destruction were sometimes grouped together and marked off by means of a measuring-line and plummet (Sa2 8:2; Isa 34:11; Amo 7:7); so that the line of Samaria means the line drawn for the destruction of Samaria; the plummet of the house of Ahab, for exterminating his apostate family; and the import of the threatening declaration here is that Judah would be utterly destroyed, as Samaria and the dynasty of Ahab had been.
I will wipe Jerusalem, &c.--The same doom is denounced more strongly in a figure unmistakably significant.
4 Kings (2 Kings) 21:14
kg2 21:14I will forsake the remnant of mine inheritance--The people of Judah, who of all the chosen people alone remained. The consequence of the Lord's forsaking them would be their fall into the power of their enemies.
4 Kings (2 Kings) 21:16
kg2 21:16Moreover Manasseh shed innocent blood--Not content with the patronage and the practice of idolatrous abomination, he was a cruel persecutor of all who did not conform. The land was deluged with the blood of good men; among whom it is traditionally said Isaiah suffered a horrid death, by being sawn asunder (see on Heb 11:37).
4 Kings (2 Kings) 21:19
kg2 21:19AMON'S WICKED REIGN. (Kg2 21:19-26)
Amon was twenty and two years old when he began to reign--This prince continued the idolatrous policy of his father; and, after an inglorious reign of two years, he was massacred by some of his own domestics. The people slew the regicide conspirators and placed his son Josiah on the throne.