The person has murdered someone that has been a problem for the person the song is about, and he believes that the person had it coming. He later realizes that he has committed murder, doubting that he had the right to murder someone, even if he believes they had it coming. By the line "I'm looking through the bible, looking for a loophole", s a metaphor for him trying to find a reason to convince himself that the murder he committed was acceptable. The feeling of guilt is always with him, so he can't be happy anymore, he is consumed by his guilt.
I think the song is about this: