The title of this work suggests perennial philosophy, but the work is devoted to relgious "truths" that the author believes are transcendent and therefore permanent. From this angle, the book is an interesting read of different religious views that have helped humans live an interesting, meaningful, and ethical lives. But "philosophy" is not really involved except incidentally. There is no use of logical clarity, no evaluation of arguments, no use of the philosphical method, nor much of any tools that philosophers normally apply. Indeed, none of the usual philosophical issues are to be found: Epistemology, metaphysics, theories of language, ethics, mind, and anthropology. But, as a digest of religious views, it does a nice job of harmonizing religious "truths" across a wide spectrum of religious thought, from Buddhism, Christianity, Islam, Judaism, and Hindu thinkers. But the consequence of this "harmonization" is reductionism of different religious structures into an over-simplified, under-stated worldview and cosmology. So, even under the rubric of "theodicy," the book fails its philosophical foundations.