“A mystic is a man who has been favored with an immediate, and to him real, experience of the divine, of ultimate reality, or who at least strives to attain such experience.”

Source: On the Kabbalah and Its Symbolism (1960), Ch. 1 : Religious Authority and Mysticism
Context: We shall start from the assumption that a mystic, insofar as he participates actively in the religious life of a community, does not act in the void. It is sometimes said, to be sure, that mystics, with their personal striving for transcendence, live outside of and above the historical level, that their experience is unrelated to historical experience. Some admire this ahistorical orientation, others condemn it as a fundamental weakness of mys­ticism. Be that as it may, what is of interest to the history of reli­gions is the mystic's impact on the historical world, his conflict with the religious life of his day and with his community. No his­torian can say — nor is it his business to answer such questions­ whether a given mystic in the course of his individual religious experience actually found what he was so eagerly looking for. What concerns us here is not the mystic's inner fulfillment. But if we wish to understand the specific tension that often prevailed between mysticism and religious authority, we shall do well to recall certain basic facts concerning mysticism.
A mystic is a man who has been favored with an immediate, and to him real, experience of the divine, of ultimate reality, or who at least strives to attain such experience. His experience may come to him through sudden illumination, or it may be the result of long and often elaborate preparations. From a historical point of view, the mystical quest for the divine takes place almost exclusively wit a prescribed tradition-the exceptions seem to be limited to modern times, with their dissolution of all traditional ties. Where such a tradition prevails, a religious authority, established long before the mystic was born, has been recognized by the com­ munity for many generations.