My interpretation is that the core argument is talked about often throughout the book, but the premises and intuitions supporting it are only mentioned occasionally. So, the audience will be aware of Steiner's claims after having read the book, and they'll walk away from the book with the feeling of having been impressed by his skill, even though they won't actually be able to recite his argument. They do get the rough gist of his argument, Phil's point is that there's almost nothing more than gist to his argument.

Additionally, Phil may have summarized. Presumably there is some redundancy within the hundreds of pages.