Revising a book requires distance. Ideally, the writer has to detach enough from the emotional content of the writing, or the love of her characters, to "hear" the story as a reader would.
Revising without this distance usually means we repeat ourselves. We run the same track over and over.
Maybe words get tweaked. But the overall sense of the story doesn't change that much.
I needed to revise a new chapter to send my writing partner this week. I tweaked words, I adjusted sentences, but I could tell I was running that familiar track of what I already knew. Something wasn't singing yet. I also (sheepishly) knew there were scenes not holding their weight, which I kept because I liked them. My chapter, after all, right?