Midrash su Esodo 6:22

(Ibid. 33:3) "the Law of fire to them": Scripture (hereby) tells us that words of Torah are compared to fire. Just as fire descends from heaven, so words of Torah were given from heaven, viz. (Shemoth 6:22) "You have seen that from the heavens I spoke to you." Just as fire "lives" forever, so words of Torah live forever. Just as fire — one who is close to it is burnt; one who is distant from it is cold and it does not afford heat, so words of Torah — if one "handles" them (for profane purposes) he goes lost; if he separates himself from them, he dies; if he toils in them, they give him life. And just as fire is utilized in this world and in the world to come, so, words of Torah. And just as fire leaves an "impression" on one's body, so Torah scholars, who toil in words of Torah are "recognized" by men in their walking, in their speaking, and in their deportment in the marketplace.