Igros Kodesh VI pg. 285)
29 Av, 5712, Brooklyn.
Greetings and blessings,
For a person like yourself, it is surely unnecessary to elaborate on the concept explained in many places in Chassidus, and also in works of Mussar: that a divine blessing [:arousal from above”] requires a fit vessel, appropriate effort on man's part [ an arousal from below']. It is absolutely obvious that one should not initiate something that runs directly contrary to the “arousal from above: for which one is [requesting and] praying.
[In light of the above,] How shocked was I to see you[r appearance] in the office of the Merkos Le'Inyonei Chinuch, that you labored and compelled your divine soul to remove, Heaven forfend, the “Image of G-d” from your face, by cutting and removing the thirteen fixtures of the beard, which correspond to the thirteen pathways of divine mercy! They are the channels for one's livelihood, as is explained in the Zohar and in Chassidus in several places. Elaboration upon this is unnecessary, especially for tone who hails from the Sephardic community who have held fast to the study of the Zohar for all time. There, no opposition ever existed to it, as did exist in several places in earlier days among the Ashkenazim.
It is difficult and burdensome for me to elaborate upon this. Surely these lines will suffice. I give you the benefit of the doubt that perhaps your intention [in cutting your beard] was as follows: You have seen and contemplated the statement of our Sages that earning one's livelihood is as difficult as splitting the Red Sea.1 It, therefore occurred to you that perhaps it worthwhile to assist the A-lmighty (Who sustains [all creatures] from the eggs of lice until the horns of the wild ox2) in His task by causing your outward appearance to resemble the gentiles. This would then make it easier for you to be given a rabbinical position, or the like.
However, even one who is not intelligent will easily understand that this is contrary to simple faith; to suggest that laxity in observance of the mitzvos of the Torah-i.e., distancing oneself from the Source [of life]-will bring the person to be granted a large flow of blessing. You should study in-depth that which is explained concerning [the verse], “[He will bless himself in his heart, saying , “Peace will be with me, though I follow the caprices of my heart] adding the watered to the thirsty.”3
It is my firm hope that the efforts that my father-in-law, the Rebbe, of blessed memory invested in you as his student and his Chossid will assist you to leave behind the aforementioned mistaken thinking. If the hand of someone else is enticing you [to cut your beard], then explain to him as well that such conduct is contrary not only to divine intellect, but also to human intellect. For every Jew believes that G-d is the Master, even of this physical and coarse world. He and only He is the one to allocate sustenance to a person and his family. Thus, the human effort [“arousal from below”] should also be consistent with this.
From on who awaits good news and blesses you with spiritual and material success, which, for a Jewish man and woman, go hand in hand,
PS: Our Nesi'im have elaborated upon [the prohibition of] cutting one's beard: Tzemach Tzedek, Shu”t Yoreh Dei'ah, 93. Tzemach Tzedek, Chiddushim leMakkos, ch. 3. Piskei Dinim on Yoreh Dei'ah, 181, sec.2. Derech Mitvosecha, 2:221b. In the book known as Amudei Arazim of Rabbi Margolis of Yerushalayim, toward the end the compiled the opinions of the later rabbinical authorities, etc., concerning all the above.
 Pesachim, 118a.
 Shabbos, 107b.
 Devorim, 29:18. This is explained in Kuntres U'Ma'aon, ma'mar 5.