''Sefer ha-Zohar'' (The Book of Radiance) has amazed readers ever since it emerged in medieval Spain over seven hundred years ago. Written in lyrical Aramaic, this masterpiece of Kabbalah exceeds the dimensions of a normal book; it is virtually a body of mystical literature, comprising over twenty sections. The bulk of the ''Zohar'' consists of mystical interpretation of the Torah, from Genesis through Deuteronomy. This eighth volume of ''The Zohar: Pritzker Edition'' consists of commentary on the end of Leviticus and the beginning of Numbers. Its most remarkable section is ''Idra Rabba''--a dramatic narrative, in which Rabbi Shim'on and his Companions gather to explore the deepest secrets of God's nature. There is a sense of emergency here, because due to human misconduct, the world is vulnerable to divine wrath. The mystical heroes seek to restore the balance in the upper worlds--aiming to stimulate a radiant flow from God's aspect of Compassion, which can soothe the irascible divine aspect and thereby save the world. The quest is perilous, and through its intensity three of the Companions tragically perish.