5 Main Themes

Everything is connected once you remove a layer or two sounds like a pretty solid theme.
I'm not sure to the exact relevance of this, but in the introduction, the authors state
that:
"This book, then, has been written from a very specific worldview, based on a few fundamental ideas:"
1. Incentives are the cornerstone of modern life.
2. The conventional wisdom is often wrong.
3. Dramatic effects often have distant, even subtle, causes.
4. "Experts"--from criminologists to real-estate agents--use their informational advantage to serve their own agenda.
5. Knowing what to measure and how to measure is makes a complicated world much less so.

So these ideas provide the theme for each chapters, and often the reoccur in other chapters as well. (They absolutely love to discuss incentives, and not just for parents picking up their kids at daycare). I took these points as the points the authors were trying to prove as well (the theses, if you will).

I think perhaps the large theme/message goes into each one of those individual themes, and that's how the entire book achieved any sense of cohesion and flow (sorry I know the hate of that word).