How can I ask a teacher to follow the textbook more closely? This term I'm taking a (graduate) course which is crucial for my degree. The teacher's plan for the course is quite ambitious and all along he's been following the structure of a given text, but he doesn't follow it completely and quite often omits (what I consider) key results from it, e.g. results which motivate or deepen the understanding of definitions or other results. To put it bluntly, he leaves a lot of gaps that the book covers nicely.

It's been a frustrating process and we're soon going to start with a very important topic and I've been wondering how to approach him about this. My idea at the moment is to ask him to follow the textbook more closely, even if by doing so we sacrifice how much we cover, but I'm looking for suggestions.

Final edit (concluding remarks): I've chosen the answer which I think gave me the best course of action and I think summarizes some of the most important points in comments and other answers. Anyone reading this thread in the future should definitely check all of them anyway. They all provided valuable feedback for me. 

I'd also like to point out that Shane's comments in chat are spot on. I believe said comments capture the exterior root of my problems, which I was unable to see at the time when the question was written. On my end I also learned a couple of important things on how to deal with these kind of situations.
You may certainly ask -- politely! -- but you should expect to be told "no", and you should accept that answer if it is given.  In most graduate courses, it is the privilege of the instructor to decide what are the important points and how to organize them.

If the course is preparation for a qualifying exam (for instance), then there may be a more rigid syllabus that needs to be adhered to.  In such a case, if the instructor were deviating strongly from the expected objectives it would make sense to complain.

As an aside: since the book presents things so well (from your perspective), you can learn the material from it and consider the lectures as supplementary.  It then seems to me that having lectures that approach things from a different perspective than that of the text is a benefit.  An instructor who parrots the text would be redundant.