This book is a major contribution to understanding the historical context and evolution of the siddhi tradition within Buddhism. Its research, speculations, and conclusions may not please everyone, but it's of tremendous value in understanding the origin of practices, divinities, and personages. The book is scholarly, loaded with footnotes, and appendices reflecting the author's research. It is very well written. While the book is not designed as an encomium to Buddhist mythology, it serves well those who wish to understand Buddhism's historical context.
Davidson's book is not for those unfamiliar with the history of India or with the development of Buddhism, but it does not require advanced knowledge to follow his argument. (I would have found it unintelligible if it did.) It is also not for the devotional reader, or for anyone in search of details of religious practices, Yogic or otherwise. For those with a serious interest in the history of a great religious tradition, however, it is worth attention.
He outlines the complicated history of India during the centuries on either side of the first Muslim invasions, describing the internal and external warfare, the rise and fall of imperial states, the shifting of trade routes, and other political, military, and economic factors bringing about material, organizational, and ideological changes. The declining status of women, particularly their place in public religion, is given considerable attention. Archeological and iconographic evidence is used when available; fieldwork in India and Pakistan has suffered from delayed publication.
Davidson then proceeds to apply this picture to the emergence of new and radical strains in Indian Buddhism and Hinduism during this long and turbulent period. He argues, convincingly, that disruption of the great monastic institutions around which Indian Buddhism had been built allowed for personal forms of religiosity to emerge. Some of these, which we know as "Tantra," had a great future within Mahayana Buddhism, but mainly outside of India. Other responses probably vanished without a trace
Davidson emphasizes that similar trends appeared in Hinduism during the same period, and argues that the esoteric traditions influenced each other in complex and subtle ways, some of which he explores Studies of popular religion in modern India are also used, including Davidson's own investigations. He also argues that organized Indian Buddhism suffered in the long term by abandoning is own traditions of philosophy, and adapting its arguments to the prevailing concerns of the time. Although this produced some interesting philosophy, the shift from salvation to epistemology was bound to weaken the appeal of Buddhism as a religion in a time of upheaval. This loss of emotional impact also helps to explain the infiltration of new and radical forms of meditation and ritual into the monastic movement itself.
I found the book fascinating, although not easy going at times. The emergence of new religious forms is often explained as a result of processes internal to the religion in question, and often blamed on the representatives of the old ways. Davidson's argument that external factors can play an equally important role suggests taking a new look at popular mystical movements in other religions. For western Christianity, a comparable work, although from a very different starting point, is Norman Cohn's "Pursuit of the Millennium," which argued for the close relationship between social and economic issues and religious movements in the later Middle Ages. Some of the "libertine" movements he describes have a certain resemblance to various manifestations of the Tantric movements in both Hinduism and Buddhism. Also consider, for example, the relation of the rise of Hasidism in the Jewish communities of Eastern Europe to the catastrophic decline of the Polish state, rather than the supposed failures of the established Jewish leadership.