Likutei Moharan 38:6/ליקוטי מוהר"ן ל״ח:ו׳

16. {“They stripped off their jewelry…. Then Moshe took the ohel (tent)” (Exodus 33:6, 7) . } Now, Moshe <also> merited the light of tefilin, as is written in the Zohar (I, 262a): “They stripped off their jewelry”—this is tefilin. “Then Moshe took the oHeL”—he took those lights, as indicated in (Job 29:3), “When his lamp HiLo (shone) over my head.”

2{“Aharon and all the Israelites saw that the skin of Moshe ’s face karan (was radiant), and they were afraid to come close to him” (Exodus 34:30) . } And this is the meaning of “that the skin of Moshe’s face KaRaN,” similar to, “it had a single KeReN (horn) on its forehead” (Chullin 60a). This is the aspect of tefilin, which is [worn] atop the forehead. Because of this “they were afraid to come close to him”—for he shone the fear upon them, as in, “Then you will understand the fear of God, [and attain awareness of the Lord].”

3This is also as our Sages taught: Whoever sins and is embarrassed by it, <his sins> are forgiven (Berakhot 12b). This is because the sin instills in a person the spirit-of-folly. But through embarrassment, he restores the mentalities, as in, “Then you will understand the fear of God,” as explained.

4And this is as our Sages taught: Whoever is brazen-faced, it is a certainty that his ancestors’ feet never stood at Mount Sinai (Nedarim 20a). For the First Man blemished the aspect of tefilin, which is an aspect of the Tree of Life, <as our Sages taught (Menachot 44a): Whoever dons tefilin merits life, for it is said> (Isaiah 38:16), “O God, [with these things] on them, they live.” And he attached himself to the Tree of Death. As a result, He drove him away from the Garden of Eden (cf. Genesis 3:24). For the brazen-faced person [is destined] for Gehennom (Avot 5:23). But when he repented, it is written (Genesis 3:21), “[God] made them leather garments”—this is tefilin .

5This is the explanation of: The ox that the First Man sacrificed had a single keren on its forehead. For by means of the sacrifice, by repenting, [Adam] merited the aspect of tefilin —which corresponds to the keirun (radiance) of the skin of the face.

6But concerning Kayin, who was from the pollution of the Serpent, it is written (Genesis 4:6), “Why is your face fallen?” This is an aspect of the tefilin’s light, which is the radiance of the facial skin. <And he brought a sacrifice> from the dregs (Bereishit Rabbah 22:5) —seeing fault in everyone. We also find: “Then He placed a mark on Kayin” (Genesis 4:15) —a keren shone from him, as explained above. This is as is written of Kayin (ibid.: 16), “He settled in Nod, kidmat (east of) Eden.” The explanation is that he did not merit Eden because he blemished the light of the tefilin. This is KiDMaT, an acrostic for Karkafta D’lo Manach Tefilin (a skull that did not wear tefilin).

7And this is as our Sages taught: Whoever is brazen-faced, it is certain that he is guilty of adultery (Taanit 7b). <As is brought in the Tikkuney Zohar,> Kayin came upon Hevel’s twin sister, as is written (Genesis 4:8), “Then, when they were in the field.”

8Thus Israel, who stood at Mount Sinai, were cleansed of their pollution, i.e., the pollution of the Serpent. But the nations, who did not stand [there], were not cleansed of their pollution (Shabbat 146a). This is, “it is certain that his ancestors’ feet never stood.” Specifically “the feet,” because they lack <the aspect of> feet, <corresponding to the Serpent’s pollution,> as is written (Genesis 3:14), “On your belly you will crawl.”

9This is as it is written: “Then God placed a mark on Kayin”—He restored their fear of him in them. As is written, “All the nations of the world will see [that God’s name is associated with you, and they will fear you].” As is written {in the Zohar }: When he repented, “then God placed a mark on Kayin” (Tikkuney Zohar #69, p.118b).