Well I am going to tell you right out front. I like your concept A LOT more than I like your current execution/writing style. Reading this was a bit of a let down to me because I could see it being so much better. Here we go with your evil critique.
Most of this is going to come out in my comments on the actual document, but here are my main problems.
I liked your narrator, but be careful with all his side comments, dialect and places where he directly addresses the reader. Those kind of things distract from the story and bloat up your writing unnecessarily. Doing it a little is great and humorous, but I think right now you are over doing it to the point that it really bothered me.
Also, if you write in first person your character
is your story and you really have to start there so you can avoid a lot of the confusion you have in the beginning. Show me Mat (who he is, where he is, what he is doing) first, at least briefly, and show me everything else.
That being said, I felt the prologue and much of the first chapter was confusing. I can understand that you want to hook with action and get to the meat of your story quickly, but you are doing it at the expense of your character, world and setting and it just doesn't work. If I don't know all the stakes (all the 'whys' and 'whats') I have no reason to care who is stabbing who. Having a flashback/flashforward to the action briefly for a hook is fine, but that is all secondary to the story itself. Personally, I feel that your concept is interesting enough that you could easily spend a chapter or two just character/world building through scenes (not long summations) and then all your action and plot would be that much better as it comes.
Rather than summing up his whole initiation and interactions with the upper angels, why not start there and show us some of this happening there by avoiding a lot of the time breaks and other points of confusion? I have about the same attention span as the average teenager (or rather the average teenager that reads for 'fun') and generally when you start to sum things up, I start skimming and I don't want to be skimming that much in the first few chapters. Either build the important information into scenes or drop it all together because I'm not reading it anyway.
Also, make sure that the character's thoughts/dialogue fit the situation or it just doesn't work.
Really, this felt to me like I was reading a sequel. Like in the last book you had Mat become an angel, get his powers and had everything firmly established through that summer and now you are quickly orientating us so we can get to the next story.
I agree that the third chapter was basically useless, especially since the guy really didn't seem to have anything all that important to say and that your dialogue/paragraphs run too long to be natural. I also agree that some of the 'core issues' Asmodemon mentioned were too quickly tossed aside and that a lot of these issues seemed like they should have come up earlier in the summer.
I think that is all the big stuff... it is all in my comments anyway and let me know if you have any questions. Like I said, I think your concept it great and something I would like to read if you can pull it off. Good luck.