Actually Robert himself has said that the song is about a prostitute that he falls for and even though he knows it's wrong to love her he can't seem to part from her so when he mentions that he can't fight the devil and says to let me sign he is referring to signing his soul over to the devil to be with the prostitute because in his mind being with a prostitute is wrong but he doesn't care because she has stoned him to his soul and his love for her has damned him in a way. I listened in an interview Rob talk about the lyrics and their meaning so that's the meaning of the song that was written by his friends and the director Catherin found it appropriate for the first movie;) But even though that is the meaning behind the lyrics for the marcus and bobby, who wrote the song, I think you can still find your own personal meaning to it. That's how we connect with music anyhow. And I figured you all should know the truth behind the lyrics if you were curious:)