@aishwisdom: Kabbalah, or received wisdom, contains many of the most mystical and profound Jewish teachings. It's not just one book, but many works, which were often compiled over centuries. The mysteries of the Kabbalah are ancient, and are discussed openly in the Talmud, although it was generally studied in private. Its study became more commonplace with the publication of the Zohar in the 13th century, and particularly after the golden years of the Tzfat school in the mid-16th century.