The path of spiritual knowledge and freedom has often been described by using the metaphor of "going to war"; hence the term "warrior." Make no mistake, though, this book has nothing to do with violence or military action. It is not a Green Beret handbook and has no photos on how to perform a proper takedown. Rather, it is a textbook and reference manual on the development of spiritual power.
Many others have traversed this same territory, and the author is a student of various paths, and so he presents a synthesis of some of the threads he has encountered: Carlos Castaneda and the Toltecs, Dan Millman, Shambhala, G.I. Gurdjieff, the Feldenkrais method, A Course in Miracles, and Neuro-Linguistic Programming are his main sources, alongside his personal experience as a psychotherapist.
The result is a very useful and well-organized distillation of the ways and means to personal power -- power over self, as opposed to power over others. People familiar with any of the above sources will find similar concepts here, but presented in a very straightforward format (as opposed to some of the storytelling styles of some of the sources). The seeking of personal power is, after all, a very practical pursuit, not something limited to stories about people who have had supernatural experiences or extraordinary teachers.
The warrior's way represents simply the most effective and efficient way of living in the world: with minimization of energy waste and maximization of available resources, achieved through honing the self down to a fine point by relentless self-examination and action. It requires discipline, nonattachment, compassion, and surrender of self to be truly free, and these things are available to anyone. Spencer's book makes this all the more clear in his drawing from many sources, showing that, truly, truth and opportunities for gaining power can be found almost anywhere you look.
All in all, a most lucid presentation and thorough description of what is expected of a person on the warrior's path. I would also recommend A Toltec Path, by Ken Eagle Feather.