I'm looking through that book again to see if I can find what you're looking for, but I'm a slow reader. I feel it's in there, but I also read around the other texts on that blog to get a wider idea of the philosophy so it might be in one of those. I suggest reading around the set: read the introductions, the philosophical sections, the appendix. The taijiquan solo set is meditation, or exercise of the mind. The Way you perform the set is more important than the postures themselves (Taijiquan is Daoism! Read the Laozi, Zhuangzi, etc.!).
Um,
My learning style is to skim the surface of a thousand fields, dive into the few that feel particularly fruitful, and integrate the whole experience. My way of learning Taijiquan was to open myself to anything related to it and just "let it go in one ear and out the other": that's how I think of the sets and meditations I practice.