Practical Kabbalah, Kabbalah Ma'asit, uses the knowledge of Kabbalah in order to directly influence natural states and actual events. Sometimes this involves summoning spiritual forces and commanding them to act in reality through techniques such as the ritual incantation of Divine Names or the inscription of such Names (or names of angels) upon specially prepared amulets.
Because of its power for good and evil, Kabbalah Ma'asit is to be employed by only the most holy and responsible of individuals and for no other purpose than the benefit of creation and the hastening of the realization of God's ultimate desire in creation.
The Ari, whose teachings form the core of Kabbalistic doctrine today, exhorted his disciples to avoid the practical arts of Kabbalah (with the exception of writing amulets), as he deemed such practice forbidden in absence of the necessary state of ritual purity.
At the time when the Temple still stood and prophets walked the earth, it was possible to purify oneself (from the impurity that issues from contact with death) with the ashes of the red heifer. However, at present, we neither have the Temple, nor the red heifer, and we are unable to purify ourselves as is necessary for practical Kabbalah to be holy and successful. The arts of practical Kabbalah when conducted by an impure person can be extremely detrimental to all involved.
The Ari's prohibition in effect deferred the practice of practical Kabbalah to such a time as when the Temple will be rebuilt and the requisite purity restored.
The Temple service was the primary framework within which the practical aspect of Kabbalah evolved. The principal rite of the practical tradition–enunciating the essential four-letter Name of God, the Tetragrammaton (commonly referred to as the NameHavayah, a permutation of its four letters, which as a word means "existence") whose correct pronunciation is today forbidden–was the centerpiece of the Temple service conducted by the High Priest on Yom Kippur.
Like other aspects of the practical tradition, the precise pronunciations and incantations of God's holy Names were passed down from generation to generation. Toward the end of the period of the Second Temple it was determined by the sages that, for fear of them being misused by the unworthy, these secrets should no longer be revealed–even in the Temple service the incantation of the Name was concealed in song–and after the destruction of the Temple they became forgotten.
By concealing the precise pronunciation of God's Names, the sages provided a precedent for those who, like the Ari, argued in later generations against the practice of Kabbalah Ma'asit.
(Indeed, the Ari's fears proved to be well-founded as in the ensuing centuries we have witnessed the emergence of pseudo-Kabbalistic movements, driven by either rank opportunism or misguided spirituality, which have compromised their followers' faith and well-being as well as the reputation of legitimate Kabbalistic pursuit.)
But there is more to be said regarding Kabbalah Ma'asit. Based on the principle set by the sages that often "our damage is our correction," the Ba'al Shem Tov saw that our present unworthiness to practice Kabbalah Ma'sit–that once found favor in the eyes of God when practiced by the worthy–is a sign from Heaven that we are now capable of reaching an even higher level of Divine service. He taught that the Jewish soul, "an actual part of God," possesses the power to influence reality and miraculously change the course of nature by means of simple faith, prayer to God, and good deeds.
There is no longer any need for practical Kabbalah, taught the Ba'al Shem Tov! The world at large, approaching the Messianic Age, has reached a higher potential state of consciousness. With the aid of connecting ourselves to the truly righteous of the generation, to those souls whose consciousness is pure and holy–and in relation to whom our own souls are individual sparks–we can even now access the infinite resources of energy latent in our souls to work miracles.
In the future, with the coming of the Messiah and the building of the Temple, the miraculous will become nature and the esoteric will become common knowledge. We will then be pure in both body and spirit and God's ineffable Name will be an inseparable part of our natural consciousness.