The flow of a math book is not like the flow of a novel. A novel should be read fluently, but math books cannot. If you are reading a novel and are somewhat distracted, you can still get the idea of the story. When you are not concentrating on math, you will get very little out of it, and it will seem more difficult that it really is.
Every word counts.
Math books are usually not repetitive, so there is little chance of picking up missed information from reading on. Writers of math texts believe that extra words and repeats get in the way of clarity. Never start in the middle of the book, the chapter, or the page. Each page assumes you have mastered the previous pages. Understand each sentence before you go on.