The Hebrew term for the passage of a soul after death into another physical form—human, animal, or inanimate—is gilgul neshamot. Although reincarnation as a doctrine is generally renounced by Jewish theologians and philosophers, the Karaites, a Jewish sect which rejected Rabbinism and Talmudism, taught transmigration of the soul. Anan ben David, who founded the Karaites in Baghdad about 765, said that all human souls have a common origin in the primordial human, Adam Kadmon, whose spiritual essence sends forth sparks which form individual souls. When the later Adam of Genesis committed sin in the Garden of Eden, his fall brought about confusion among higher and lower souls throughout creation, which resulted in the need for every soul to pass through a series of incarnations. Although Anan ben David's teachings were severely criticized as contrary to Orthodox belief, gilgul became a part of the Kabbalah, the compilation of mystical works collected in thirteenth-century Spain. Transmigration of souls is also a universal belief in Hasidism.
According to Alan Unterman in his Dictionary of Jewish Lore and Legend (1994): "Transmigration gave a new meaning to many aspects of life.…The deaths of young children were less tragic, since they were being punished for previous sins and would be reborn in a new life.…Proselytes to Judaism were Jewish souls which had been incarnated in Gentile bodies. [Transmigration] also allowed for the gradual perfection of the individual souls through different lives."
The Zohar (Hebrew for "Splendor"), the main work of the Kabbalah, describes the esoteric reality that lies behind everyday experience, and insists that the real meaning of the Torah lies in its mystical secrets. Although tradition declares Rabbi Simeon ben Jochai (c. 80 C.E.) as its author, later scholarship acknowledges the contribution of Rabbi Moses De Leon (1240–1305) and other Hebrew scholars in the thirteenth century. The Zohar states that since the human soul is rooted in the divine, the redemption of the world will be achieved when each individual has undergone the process of the transmigration of souls and completes his or her task of unification. Because humans cannot know the Most High's plans for each individual, they cannot know how they are being judged at all times, both before and after coming into the world and when they leave it. Because the goal of all human souls is to reenter the absolute from which they originally emerged, it is necessary for them to develop the level of perfection that will find them worthy of reunion with God. Since it is unlikely that such perfection can be achieved in one lifetime, the souls must continue their spiritual growth from lifetime to lifetime until they are fit to return to the divine.
Although the study of the Kabbalah undergoes cycles of popularity and esteem, reincarnation is not generally taught today in the three main branches of Judaism—Reform, Conservative, and Orthodox—but is accepted by those in the Hasidic sect. Rabbi Yonassan Gershom, a neo-Hasidic rabbi, has said that although Jews are generally reluctant to speak of their personal spiritual experiences in public, it doesn't mean that some of them aren't having memories of past lives.
"There are many teachings about reincarnation in Jewish mysticism," Gershom said. "The Hebrew word gilgul comes from the same root as the Hebrew word for 'circle' or 'cycle.' So the essence of its meaning is similar to the ideal of the Wheel of Karma."