This is from 2 Kings 21:1-17; 2 Chronicles 33:1-20
Manasseh seems to be the opposite of his father Hezekiah. He seems to be going out of his way to do evil. He rebuilt all of the pagan high places that his father destroyed and also added some new ones. He also made Asherah poles. He made altars to Baal. He also worshipped the stars of heaven.
As it that weren’t enough, he went and put pagan altars inside the Temple itself! And, as if that weren’t enough, he went and offered his sons as a sacrifice to a false god on an altar (possibly inside the Temple too, the Bible doesn’t say.) (This guy is definitely NOT going to win Judah’s Father of the Year Award!) He also seemed to want to know the future, no, not as a stock forecaster or anything like that, but the type where you go to mediums (fortune tellers) and wizards.
Worst of all, the people seemed to have followed him (whether out of fear of crossing him or because they liked what he did) in his bad ways. This made God mad. Manasseh had done what the heathen kings of Ammon had done before Israel beat them. Their sin was so bad that God had sent Israel to defeat them to punish them. Now God said that because of Manasseh and the people of Judah for following him, that Judah would fall.
Manasseh wasn’t done, however, with his crimes. He was also recorded to kill many innocent people in Judah. The people said that he filled Jerusalem from one end to the other with blood. It was during his reign, and no doubt at his orders, that Isaiah was killed. His reign was longer than most kings too.
Then, one day, Assyria came and took Manasseh away and took him to Babylon and put him in prison. There, he cried out to the true God and asked for help. God heart him and helped him get released. This was no mere jailhouse conversion.
Manasseh turned his whole life around. He got put a new wall around Jerusalem. He got rid of the idols and threw the idols out of the high places. He took the idols out of the Temple. He commanded everyone to only serve God. People still sacrificed in the high places, but now only to the true God. Also, he offered a thanks offering to God in the Temple. God had changed Manasseh completely.
Though Manasseh had done wrong, God didn’t wipe out his line, both out of respect for David whom he had promised that he would keep his line going, and because, though Manasseh couldn’t have deserved it, God used Manasseh to become an ancestor of Christ Himself. (He is listed as Manasses in Matthew Chapter 1.) The forgiveness of God is awesome! He can forgive anyone, no matter what evil they may have done! (However, it should be noted that Manasseh’s conversion happened too late to have a lasting influence on Manasseh’s son Amon (though he may have, along with Manasseh’s father Hezekiah, have affected Josiah, his grandson, and the last good king of Judah) nor on the bad trend that was happening in Judah that would lead to its downfall. Thus, we should be sure to get right with God now and not put it off another day!)