The roots of Kabbalistic tradition can be traced back to the ancient prophetic experience of our ancestral forebears–Abraham, Isaac, and Jacob. The wisdom and insight born of their intimacy with the Divine formed the basis of the spiritual legacy passed on to their children, the twelve tribes of Israel. The ultimate verification of this legacy came at the moment when Israel stood at the foot of Mount Sinai, the heavens parted and the spirit of God descended from on high amidst thunder and lightning fire. In revealing Himself to the entire community of Israel, God in essence laid bare the hidden core of Kabbalistic truth which up to that point had been the privilege of a select few. At that very moment, the verse tells us, Moses ascended up the mountain into a thick darkness where God privately revealed to him the complex of Divine wisdom and law that was to fill the void that remained after His retreat back into the heavenly sphere.
The wisdom which Moses received on Sinai and later passed on to his people was comprised of both esoteric and exoteric elements. The exoteric tradition–or niglah (that which is "revealed")–became the identified focus of Jewish life, both in study and practice, for generations thereafter. It is this tradition which we are familiar with through the classical works of Jewish law and scholarship–chief of which is the Talmud. On the other hand, the esoteric tradition, known as nistar (that which is "hidden"), was transmitted to a select few in each generation suited for initiation into its mysterious depths.
This tradition, which is the basis of Kabbalah, wove its way like a hidden thread through the course of Jewish history. At providential points throughout that history, this thread would periodically surface so as to embellish the evolving spiritual consciousness of our people. Interpreted by men of unusual vision and intelligence, this tradition slowly found its way into written form as works appeared expounding upon both its theoretical and practical aspects.
The traditional terminology employed in referring to these two distinct aspects of Kabbalistic inquiry is that of Kabbalah iyunit ("contemplative Kabbalah") and Kabbalah ma'asit ("practical Kabbalah"). Although we will see that this distinction can often be quite arbitrary, it will help us to isolate various trends within the development of Kabbalistic tradition.