- You have to be good at revising before you even have an editor, so you're presenting your best work;
- If you're a first-time author, your manuscript needs to be in publishable shape because an editor doesn't know if you can't revise and has to assume your book isn't getting better; and
- Writing and revising require different hats (say, Dr. Seuss vs. a construction hardhat).
Then she writes a new draft and repeats. Lots of times. She makes major changes. Kills characters. Changes endings. Changes themes.
Follow your muse, but recognize that stories often change.