-Menasha was the most evil of all kings of Yehuda. We are going to explain what promoted him to take these actions.
-People are created with free will.
-Meaning when a person does something wrong he can always rationalize it too some degree. There is always a side in his mind that maybe it is not so bad.
-This is all necessary for if something was obviously evil it would be very easy not to do. Since the challenge would be limited so would the reward.
-Menasha was born with an extra ordinary amount of fear of Heaven. When ever he would do something wrong it was clear to him that it was wrong. What he was trying to do was get back to a state where he would have free will.
-Meaning, take the few moments you feared G-D multiply it many times and keep that as a constant state. This is what Menasha had to deal with.
-By constantly sinning he wanted to destroy this feeling little by little.
-Just as Chzal said, when some one sins once then twice it becomes permissible in his eyes.