Manasseh began reigning as vice-regent with his father Hezekiah when he was 12 years old in 697 B.C. This arrangement continued for 11 years until Hezekiah died in 686 B.C. For a total of 55 years Manasseh was king of Judah. He reigned longer than any Hebrew king, and he was Judah's worst king spiritually.
"Manasseh was the Ahab of Judah' and the antithesis of the great David."129
Among his other serious sins Manasseh built idol altars in Yahweh's temple (v. 4). This diminished the reputation of Yahweh considerably. Canaanite idolatry, Ahab's Baalism, Canaanite astral worship, Ahaz's human sacrifice, and Saul's spiritism were all heresies he revived even though the Law of Moses condemned them (Exod. 20:3-5). He did not follow David's example, he defiled the temple with idolatry, and he rejected the Mosaic Covenant. Thus he not only acted opposite to Hezekiah, but he also scorned the examples of Moses, Joshua, David, and Solomon. In his day the people were more wicked in their religious practices than even the Canaanites had been (v. 9).
Isaiah and Micah were two of the prophets that God had used to warn the nation before Manasseh's reign, and their influence undoubtedly continued after their deaths. According to Jewish tradition Manasseh sawed Isaiah in two (cf. Heb. 11:37).130But we have no record that any prophets ministered during Manasseh's reign with the possible exception of Nahum whose ministry was against Assyria.131
Not only did Manasseh apostatize himself, he also led the nation in departing from God (v. 11). The "line of Samaria"(v. 13) refers to the righteous standard God had used to measure Samaria's fidelity to His will. The "plummet of Ahab's house"(v. 13) was the same plumb line of righteousness by which God had judged Ahab's family. God would abandon His people temporarily but not permanently (v. 14; cf. Deut. 28:63-64).
Manasseh's murders included those of his own children (v. 6) as well as Isaiah. Manasseh's many sins stained Judah deeply. Even Josiah's later reforms could not avert God's judgment (23:36). His burial reflects the fact that his behavior resulted in his people esteeming him lightly. God had disciplined him personally (cf. 2 Chron. 33:11-13), and he had become a channel of God's discipline for Judah.
Perhaps we should view the fact that God allowed such a wicked king to rule his people so long as an evidence of His longsuffering desire that Manasseh and Judah would repent. The king did repent later in life (2 Chron. 33:15-19). His long life was not a blessing for faithfulness as Hezekiah's had been but an instrument of chastening for Judah.
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