From Moshe Hallamish, “An Introduction to the Kabbalah,” State University of New York (SUNY) Press, 1999 (trans. Ruth Bar-Ilan), Chapter 4. (End notes not included.)
Another form of mystical preparation that is repeatedly mentioned in kabbalistic literature is the many-sided state of silence. The disciples of the ARI state in his name that "whoever sat for forty days in a row without verbalizing any mundane thought, will attain wisdom and comprehension." Indeed, R. Hayyim Vital lists silence as the first condition for attaining wisdom. In this connection it must be noted, without going into details, that the very fact that silence is specified as one of the conditions-sometimes in association with midnight as the propitious time for gaining comprehension-attests to the importance of solitude.
This calls to mind the stand taken by Rabbi Isaac of Acre, according to which the prophet's public calling interferes with the process of his devekut. Hence, if the prophet wishes to resume the prophetic state, he ought to “stand before God in solitude, divesting his soul of the sensibility with which it clothed itself.” Occasionally, Rabbi Isaac stretches this point to the extreme by advocating the mortification of the flesh.
Among the Bratslav Hasidim, the notion of hitbodedut, “solitude with God,” led to an intricate practice. Rather than discussing it in detail, let me introduce two passages taken from a Bratslav manual of hanhagot. Likkutey 'Eisot, s.v. “hitbodedut,” par. 13 (and, in parallel, Likkutey Moharan, part 2, par. 25), reads as follows: “Solitude is a great virtue and a proper and very straight way by which to draw nearer to God, blessed be He. And every one ought to set aside a few hours a day, during which he will pour out his heart to God in the vernacular, such as Yiddish, which is spoken in these countries.... For it is easier to converse well in the spoken language. And whatever he feels at heart, he will communicate to God, blessed be He, such as complaints and excuses and placating words and supplications, so that he will be able to approach Him. And every one should do so to the extent of his awareness of the flaws of his heart and how much he is distant from God.... It is only by conducting themselves in this fashion that the greatest of the zaddikim [the Hasidic rabbis] attained their spiritual level.” In par. 20, the author proceeds along the same lines: “When the Holy One, blessed be He, helps the individual to practice solitude, he can converse with Him as one does with a friend. And one must train oneself to converse with God as one does with his rabbi or his friend, for God is everywhere.”
In conclusion, it is appropriate to cite the words of Rabbi Kook: “The greater the individual, the more he must search within himself ... so that he must devote himself to solitary meditation, to the elevation of ideas, the deepening of thought, and the liberation of knowledge, so that eventually his soul will reveal itself to him... Then he will find bliss, will rise above all base things, and transcend all things, by reaching the state of equanimity and unity with all things ... to the point of annihilating the yesh, the 'substantiality,' in the innermost recesses of his self... Then will he know every glimmer of truth and every glitter of honesty wherever it flashes.”