I strongly agree with the feeling that there is a hole in the current material. At the same time, given the glimpses I've had of the other chapters and their sections, I wonder if we "just" need to get through the rest of the book.
The current state of The Book and our progress through it as a community specifically reminds me of being at school: the lessons build on each other, and it always takes a certain amount of material covered before you start to really make sense of things and "refactor", almost, your prior understanding.