I know you're wondering... why is Matt's name first when I'm doing the majority of the writing? Here's a post he wrote about coauthored books. He's absolutely more than an editor on this book (and we also need his name to be first on every book in this multi-author series so that they're shelved together in bookstores and libraries). Basically, we plotted the book together - there is no way I could have come up with a plot this tight on my own - then for the past three years I would write a section, send it to him, he'd make a few tweaks and comments, then I'd implement his comments and write more. There's a few sections he's rewritten already, and I'm sure there will be many more bits when we get into draft 4... my 'this is my baby!' author side hopes it won't be too much, but Matt's changes always make the book stronger. Certainly the whole world of the ruahim is his brainchild, he is a fantastic worldbuilder and this series is only going to be as strong as it is because of his guidance.
He is an excellent editor, btw, if you can employ him, you definitely should! I'm very blessed that with this series he just takes a cut of the royalties and I don't have to pay him out of pocket.