Musar do Psalmów 121:5

One recites the blessing, "Blessed are You, Lord our God, King of the Universe, who sanctified us with His commandments and commanded us to affix the mezuzah." And one must place it on the right, as it is stated: And you shall write them on the doorposts of your house (beitecha) and in your gates — the way you enter (biatecha). And when a person lifts his foot [to begin walking], he lifts his right foot first (Yoma 11b:9). And all entrances are obligated in [having] a mezuzah, except for entrances that are not the way of respect [such as bathrooms]. And it is the obligation of the one living in the house to place a mezuzah. As Rav Mesharshiyah said, "Affixing a mezuzah is the obligation of the resident." And that is even though the house is not his, but only rented by him. And when he leaves, he may not take it in his hand and leave; rather, he must leave it there. And this is the case if a Jew will [replace him] in the house. But if a gentile [will replace him], he may take it and leave. As we follow the textual version in Bava Metzia (102a:2) in the chapter [entitled] HaShoel: Come and hear — One who rents out a house to his fellow, it is incumbent upon the renter to prepare a mezuzah for it. And when he leaves, he may not take it in his hand and leave. But if it is [the house of] a gentile, he may take it in his hand and leave. And there was an incident in which a renter took his mezuzah in his hand and left; and he buried his wife and two sons. And we follow the textual version in the chapter [entitled] BeMeh Madlikin (Shabbat 32b): For the sin of mezuzah do a person's sons and daughters die when they are young, as it is stated: the blood of the souls of the innocent poor (Jeremiah 2:34), and next to it is: you did not find them breaking in. The understanding is that because they made entrances like a thief’s breach, without a mezuzah, their innocent poor, who are one's sons and daughters, died. And we place them at the entrance on the outside. For the attribute of the Holy One, blessed be He, is not like the attribute of a king of flesh and blood. The attribute of flesh and blood is that a king lays down inside his room, and his servants protect him from the outside, whereas the Jewish people, who are the servants of the Holy One, blessed be He — as it is stated: For it is to Me that the children of Israel are servants (Leviticus 25:55) — lay down inside, and the Holy One, blessed be He protects them from the outside. As it is stated: The Lord is your keeper, the Lord is your shade upon your right hand. The Lord will guard your going and coming now and forever (Psalms 121:5, 8).

He then cited, “These are the sons of Tziv’on, Ayah and Anah — the same Anah who found the mules (yeimim) in the desert.” “The word yeimim is written missing a yud (ימם).” The concept here is that there is a certain kind of destructive spirit, Heaven spare us, that focuses in particular upon those guilty of immoral acts from which mamzeirim are produced (i.e., adulterous or incestuous relations bearing the penalty of excision). These spirits are called yeimim. It is written without a yud to indicate that they were created on the eve of the first Shabbos just at dusk (relating yeimim to yom — day; it is plural but missing the plural yud to indicate that it is doubtful to which day this creature belongs). The proper place of these destructive spirits is upon the high mountains, where no seed or tree can be planted. That barren region is their proper place and these are the strange creatures that Rabbi Yitzchak saw. Anah, mentioned in the verse above, once visited that mountain where these creatures adhered to him. Therefore, as the Sages tell us in Pesachim (54a), he himself gave birth to mamzeirim and that he also was the first one to graft different species and produce the mule (a hybrid of a horse and a donkey). The Zohar mentions in the continuation of that passage that all desolate mountains are their dwelling place, however, concerning those who engage in study while they travel it is written, “Hashem your shelter is at your right hand” (Tehillim 121:5). Nevertheless, a person should avoid places where there is no human habitation.