This book deals with the "Book of Splendor" (Sefer ha-Zohar), the greatest achievement of Kabbalah and one of the most influential sources of Western mysticism.
Worth reading for the outrageous final section (on Christian influence in the Zohar). Really radical stuff. The first section, on messianism, is brilliant. Second section is pure philology — skippable, unless you're into that sort of thing. Has a nice appendix detailing the evidence for T. Abulafia as Rashbi.