In this book, Dr. Rachel Elior does a masterful job of reconstructing the origins of early (Merkavah) mysticism, tracing it to the priestly spirituality that shaped such Biblical books as Ezekiel and Isaiah, tracking its evolution in Apocalyptic works such as I Enoch, Jubilees and the Testament of Levi, its mutation into a dualistic, secterian priestly mysticism as expressed in the Dead Sea Scrolls, and finally being "rabbinized" through the Hechalot literature of Merkavah mysticism.
Elior makes a compelling argument, collecting the available data and giving it a coherent, compelling interpretation. The resulting narrative is so neatly done, in fact, that one is left doubtful only in that it seems so logical that it must, on some level, be an oversimplification. History just isn't usually this tidy. That said, any criticism I could offer would only be only peripheral points. Her thsis seems very sound to me and melds well with the data. This is therefore a very important book, one that dramatically advances our understanding of early Jewish mysticism.
It is an important book, but not a great one, for the simple lack of an assertive editor. This 265 page book needed only to be about 175 pages. The constant repetition of ideas, points, and the same illustrative texts, over and over again, is both tedious and unnecessary. Elior feels compelled to review the same conceptual clusters (four directions, sevens, shavuot, the solar calendar of weeks divided into 13, priestly-angels)laundry-list like, every few pages. The Rabbinic text Chagigah 2:1 must be cited, en toto, at least four times.
But this stylistic shortcoming should not prevent one form reading this work. Just be prepared to scan a bit in order to get to the pithy parts.