I don't know anything about the Theosophical Society but I guess it was some kind of occult or spiritualist society. The premise of the book is that if you can see people's auras, then you can see colorful expressions of their thoughts and feelings in their auras.

The book certainly looks interesting to read but I'm here for the art. The reason this book is, for me, so wonderful, is for the gorgeous full-color reproductions of these paintings of what Besant and Leadbeater claimed to have seen in other people's auras.

They are truly magnificent works of art, regardless of their provenance or basis in reality. According to the producers of this reprint, the paintings themselves were very influential, particularly in the history of abstract art.

Here are two examples, both being representations of "the intention to know". The first one is the beginning of somebody wanting to know something and the second one shows greater determination as, perhaps, the first efforts resulted in an unsatisfactory answer.