The Name שד"י on the Mezuzah Subdues the Destructive Force רי"ב that Looks into the House and Wants to Kill All of Its Inhabitants
Following this enlightening path, we will proceed to explain the rationale of Yaakov Avinu for employing the name שד"י when praying for the safety of the shevatim who were returning to Mitzrayim to meet the viceroy, Yosef. We will refer to a fascinating aspect of the name שד"י presented by the Imrei No’am (Bo 25) in the name of the kabbalists. Whereas the mezuzah with this special name inscribed on it is located on the right side of the doorway, it is opposed by a demon located on the left side of the doorway. This subject is discussed in the siddur of the Arizal arranged by the divine kabbalist Rabbi Yaakov Koppel, ztz”l, in relation to the significance of the mezuzah. We learn that the “nachash hakadmoni”—the primeval serpent in Gan Eden—the embodiment of the Satan, has a destroyer named רי"ב. It stands behind the front door of the house and looks inside casting an “ayin hara”—an evil eye—on the people dwelling within with the intent of killing them. It would succeed were it not for the divine protection and assistance afforded the household by the mitzvah of mezuzah. The sacred names inscribed on the mezuzah annul the force of the destroyer רי"ב with their kedushah preventing it from harming those dwelling in the house.
This is the deeper meaning of the passuk (Tehillim 37, 32): "צופה רשע לצדיק ומבקש להמיתו ה' לא יעזבנו בידו"—the wicked one watches for the tzaddik and seeks to slay him. But Hashem will not forsake him to his hand. How so? The gematria of נח"ש (358) plus its destroyer רי"ב (212) equals רש"ע (570). Thus, the passuk states that this wicked force standing behind the door and watching the tzaddik dwelling inside the house intends to kill him with its “ayin hara.” In the merit of the mezuzah, however, Hashem will not allow this to happen. This concludes his sacred insight. Then the Imrei No’am adds the following: In my opinion, this is alluded to by the passuk (Devarim 17, 8): "דברי ריבות בשעריך"—in other words, the klipah called רי"ב stands by the doorway
