The Zohar (Vol. 2, 89b) teaches, “Gehinnom has no control over the world on Shabbos.” This means that Shabbos is a day of peace and rest even for the deceased condemned to suffering in Gehinnom. They, too, are given a respite one day a week, on Shabbos. The Zohar proceeds to discuss the verse, “Do not kindle a fire in any of your residences on the day of Shabbos” (Shemos 35:3). The Gemara (Shabbos 70b) raises the question of why the Torah singles out the prohibition against kindling fire on Shabbos from among all thirty-nine melachos (forbidden activities) of Shabbos. The Zohar answers this question by explaining that the fires we kindle here on earth correspond to the fires of Gehinnom. By refraining from kindling fire on Shabbos, we keep Gehinnom “turned off” and ensure that the souls in Gehinnom are given their weekly respite, and this is the meaning of the Torah’s warning to avoid lighting fires on Shabbos.
Furthermore, the Zohar continues, this pasuk forbids lighting fires on Shabbos afilu b’gufa — “even in one’s body,” referring to anger. When a person gets angry, he kindles the fire of Gehinnom within him. Indeed, the Ramban writes in his famous letter (Iggeres HaRamban) that when a person becomes angry, “all types of Gehinnom control him.” And thus on Shabbos, when we are to refrain from kindling all types of fire, we must also exercise special care to avoid kindling fire through anger. Part of our observance of Shabbos is to avoid becoming upset and angry, and to remain calm and composed.
What might be the reason for this obligation? What does avoiding anger have to do with Shabbos?
Shabbos observance serves to reinforce our emunah, our faith that Hashem controls the world, and a person who becomes angry over something that occurred demonstrates that he regards himself as the one who controls events. Indeed, the Gemara (Shabbos 105b) describes anger as “a foreign deity in a person’s body.” Anger is a type of avodah zarah (idol worship) in that one who grows angry fails to acknowledge G-d’s control over the world.