I think everyone approaches his songs like this differently. This songs sound on the whole, I believe, as others have said perfectly captures how he felt at the time of recording. I once saw an interview on John when he was young, and he was talking about Hendrix. He said that he could tell how Hendrix felt in every song, because he became one with his guitar and the song. I think John has done exactly that with this song, and album. I think its genius.
I find this album very hard to listen to, both because of what John was like then, and how bad some of it sounds...Though, in terms of writing, some songs off the album aren't bad. While the vocals are largely unintelligible and impossible to interpret in this song, this song is extremely emotive...It's so expressive, it shows all of John's suffering, and exactly why he needed to get clean