We dive deeper into a culture by studying its language. This is also what the book is about, exploring the Japanese's psych.
First, technically, gained a better picture of what elements are associated in a Japanese sentence. And besides an analysis of all parts that made up the language, the author offered explanations with cultural narratives.
Humans are grown from mother nature, hence our inner-state should harmonize along with it, is particular to the Japanese way of perceiving the interactions and roles played with our surroundings. Japanese language is build upon such vital relationship. As an example, the intransitive forms of verbs, which have greater importance compare to other languages, is a manifestation of such ingrained subconsciousness.
As a comparison, English has far more emphasis on the fact of a subject acting upon an object. Humans are in direct control over and acting onto nature, became the central mentality. In English, the form transformation from transitive to intransitive verb follow simple rigid rules and therefore has less varieties compare to Japanese.
Where Japanese counterpart thinks that nature is the agent doing magic most of the time, and humans are simply passively sensing through the flux of her work. Since, they think, human are just part of nature, as a result, language expressions also complies to her original form of arrangement. Such mentality is well reflected in the daily use of the language.