i.e. He was convinced by his own experience of God's power, justice, and goodness, that Jehovah alone was the true God, and not those idols which he had worshipped, by which he had received great hurt, and no good.
Related Commentaries of 2 Chronicles 33:13
2 Chronicles 33:13
13 And prayed unto him: and he was intreated of him, and heard his supplication, and brought him again to Jerusalem into his kingdom. Then Manasseh knew that the LORD he was God.