A comprehensive, yet concise survey of the historical development of Jewish mysticism in both its devotional, or practical side, and its intellectual, or speculative side, along three lines (theological, psychological and ethical) throughout four clear epochs (the biblical period; the period of old Jewish esoteric teaching; the period of the Kabbalah proper, with a very clear explanation of the Zohar; and the era of Hassidism). The book's final chapter includes brief mention of the non-Jewish movements similar to the Kabbalah.