In the book, Okakura emphasises that tea taught the Japanese many things, including the simplicity that can be seen in Japanese art and architecture.
One of the most famous quotes from the books concerns teaism—a word that Okakura coined himself and which he defines as "a religion of aestheticism":
Teaism is a cult founded on the adoration of the beautiful among the sordid facts of everyday existence.
In addition to the above-linked version, you can find a free, no-frills copy at Project Gutenberg, or view a nonprintable PDF with fancier typesetting.
A cup of humanity.