The prophets were able to see into the world of Atzilut, although it was completely clothed in the lights of Beriya when they saw it. Ezekiel lived after the destruction [of Solomon's Temple], and he therefore only received prophecy from Atzilut after it was clothed in Beriya, with the lights of Beriya itself clothed entirely in Yetzira. After Haggai, Zachariah and Malachi, prophecy ended completely, and only Ruach HaKodesh remained…
After this, the lights of Atzilut and Beriya were no longer revealed at all. This is the meaning of the teaching that after Haggai, Zechariah and Malachi, prophecy ended completely, and only Ruach HaKodesh remained.
This [Ruach HaKodesh] consists of a transmission of the lights of Yetzira itself, as well as lower levels. Attaining this level is called "Ascending to the Orchard [Pardes]." This refers to Yetzira, which is called "the Universe of [the angel] Meta‑tron".
There are given techniques through which one can open the gates of the physical world so as to enter Asiya and Yetzira. These consist of Unifications (Yechudim) and prayers pertaining to the World of Yetzira and its ten sefirot. It is these techniques that are taught in the Chapters of Hekhalot, and these practices were used by Rabbi Nehuniah, Rabbi Akiva, Rabbi Ishmael, and the members of the Great Assembly. Use of techniques involving the universe of Asiya…does not bring any enlightenment…
These techniques were then forgotten. Besides this, the ashes of the Red Heifer [needed to attain ritual purity] were lost in the period of the later Talmudic sages, during the generation of Abaya and Rava [who lived in the Fifth Century], as mentioned in the Talmud. After this, they no longer made use of these techniques to ascend to the Orchard.
From then on, people only made use of techniques involving the universe of Asiya. Since this is the lowest of the universes, its angels have only a little good, and are mostly evil. Besides this, this is a level where good and evil are closely intertwined [and it is very difficult to separate them]. This does not bring any enlightenment, since it is impossible to perceive good alone, and one's perception is therefore a combination of good and evil, truth and falsehood.
This is the significance of the Practical Kabbalah. It is forbidden to make use of it, since evil necessarily attaches itself to the good. One may actually intend to cleanse his soul, but as a result of the evil, he actually defiles it. Besides polluting his soul, he will also be punished…
Even if one does gain some perception, it is truth intermingled with falsehood. This is especially true today, since the ashes of the Red Heifer no longer exist. [Since one cannot purify himself,] the uncleanliness of the kelipot attaches itself to the individual who attempts to gain enlightenment through the Practical Kabbalah.
Therefore, "he who watches his soul should keep far from them". For besides polluting his soul, he will also be punished in purgatory (Gehinom). We also have a tradition that such an individual will be punished in this world. Either he or his children will become sick, will be impoverished, or will become apostates. Learn a lesson from Joseph Della Reina and Rabbi Shlomo Molcho, who made use of the Practical Kabbala and were destroyed from the world.
All this is because of the above-mentioned reason. This involves a realm where there is no good devoid of evil. Besides this, it involves coercing angels with oaths against their will. These angels retaliate by enticing this individual, draw him into evil ways until his soul is destroyed.
Beyond this, the methods involving these oaths were concealed by earlier generations, and we are not well-versed in the proper techniques. One must therefore keep himself far from these things.
For a link to the Works of Rabbi Chaim Vital, click here. For more information on the Life of Rabbi Chaim Vital, click here.
[Adapted from Shaarey Kedusha 3:6; excerpt from "Meditation and Kabbalah" by Rabbi Aryeh Kaplan]