After his friend dies, Blaze decides to continue with the "one big plan" that George had been planning before his death. To motivate himself in this endeavour, he talks to himself as George would. This self-motivation starts off as a sort of security blanket at first, but turns into something more sinister as the poop hits the fan, further into the book.
Reading about a dumb guy as he get his head round something serious might get a little boring after a while, so King cuts between the present day of the book (the early 80s) and Blaze's unpleasant childhood. The back story we get about Blaze acts as a sort of explanation of Blaze's actions, and tells us of the underlying futility of much of Blaze's life to that point. This back story has been done better in other books, but it works well within the confines of the story as a whole, I think.
As I said earlier, I couldn't get into this book. I know we're supposed to like Blaze (and I liked him a lot more than George), but I still didn't like him all that much. He's a naive, silly guy who is easily led into doing things he knows are wrong. This might sound harsh, but I couldn't bring myself to root for him because of the state of mind that he has.