“King Ardavan IV of Parthia sent a pearl of purest radiance to Rabbi [Yehudah ha-Nasi] and requested: Send me something equally precious in return. Rabbi sent him a mezuzah. The king sent back word: I sent you something beyond price, and you sent me something that sells for a debased coin of no value! Rabbi replied: My desirable things and your desirable things are not to be compared. You sent me something that I have to guard; I sent you something that guards while you lie asleep, as is said: [Keep, my son, your father’s command, and do not abandon your mother’s teaching. Bind them on your heart at all times, garland them round your neck.] When you walk about, it will guide you, when you lie down, it will guard you, [when you wake, it will converse with you] (Proverbs 6:22)” (JT Peah 1:1, 15d).
“[When] Onqelos the son of Qalonymus became a convert, the Emperor sent a contingent of Roman [guards] after him but he enticed them with scriptural verses and they became converted…. So they took hold of him; and as they were walking on he saw the mezuzah which was fixed on the doorpost and he placed his hand on it saying to them: ‘What is this?’ and they replied: ‘You tell us.’ He said, ‘According to the way of the world, a king of flesh and blood dwells within, and his servants keep guard on him without; but the blessed Holy One, it is His servants who dwell within while He keeps guard on them from without; as is said: YHWH guards your going and coming, now and for evermore (Psalms 121:8). Then they, too, were converted. [The Emperor] sent for him no more” (BT Avodah Zarah 11a).
“שַׁדָּי (Shaddai)—שׁוֹמֶר דְלָתוֹת יִשְׂרָאֶל (Shomer delatot yisra’el), Guardian of the doors of Israel” (Kol Bo 90, 101:4).
He who dwells in the Most High’s shelter, in the shadow of שַׁדַּי (Shaddai) lies at night—I say of YHWH, “My refuge and bastion, my God in whom I trust.” For He will save you from the fowler’s snare, from disastrous plague. With His pinion He shelters you, and beneath His wings you take refuge, a shield and a buckler, His truth. You shall not fear from the terror of the night nor from the arrow that flies by day, from the plague that stalks in darkness nor from the scourge that rages at noon. Though a thousand fall at your side and ten thousand at your right hand, you it will not reach…. No harm will befall you, nor affliction near your tent (Psalms 91:1–7, 10).
“Afflictions of the children of Adam (2 Samuel 7:14). These lure human beings at doorways, wells, and toilets. Therefore, if a person places the Holy Name at his doorway—if שַׁדָּי (Shaddai) is inscribed in its supernal crowns—they all flee far away from him, corresponding to what is written: No affliction will draw near your tent (Psalms 91:10). What is affliction? Afflictions of the children of Adam” (Zohar 3:76b).
“שַׁדָּי (Shaddai) of the מְזוּזָה (mezuzah), doorpost, chases away the שֵׁדִים (shedim), demons, and מַזִּיקִים (mazziqim), destroyers, at the gate” (Zohar 3:251b).
“She is the gate by which one must enter all wisdom, and every [divine] appellation, and הֲוָיָה (Havayah), to enter each and every sefirah. She is the knowledge of everything, and without Her no creature has permission to ponder any knowledge in the world. Of Her it is said: זֶה (Zeh), This, is the gate of YHWH (Psalms 118:20)….
Shekhinah is the gate onto which the mezuzah is affixed [one of the many appellations of Shekhinah is זֶה (zeh), ‘This’ (masculine pronoun), or זֹאת (zot), ‘This’ (feminine pronoun), perhaps because as the Divine Presence She is constantly right here, see Zohar 1:49b; 2:11b–12a; 3:8b]” (Zohar 3:256b, 258a, Ra’aya Meheimna Pineḥas).
“Rava said, The proper performance of the mitsvah is to fix it in the handbreadth nearest to the street. Why?—the Rabbis say, So that one should יִפְגַּע (yifgga’), encounter, a mitsvah immediately [on one’s return home, cf. Genesis 32:1: And Jacob had gone on his way, and messengers of God יִּפְגְּעוּ (yifggu), accosted him]; Rabbi Ḥanina of Sura says, So that it should protect him [and his entire house from מַזִּיקִין (mazziqin), destroyers (Rashi)]. Rabbi Ḥanina said, Come and see how the way of the blessed Holy One differs from that of flesh and blood. According to the way of flesh and blood, the king dwells within, and his servants keep guard on him from without; but with the blessed Holy One it is not so, for it is His servants that dwell within and He keeps guard over them from without; as is said, [Look, He does not slumber nor does He sleep, Israel’s guard] YHWH is your guard, YHWH is your shade at your right hand (Psalms 121:4–5)” (BT Menakhot 33b).
“Rabbi Yehudah son of Rabbi Yose said, ‘A doorway that bears a mezuzah: no demon—neither accuser nor evil spirit—can approach, because the blessed Holy One watches the doorway. Even when the destroying angel has permission to harm, he lifts his gaze and sees the name of the Omnipresent poised over the doorway, as it were—and He will not allow the Destroyer to enter your houses to strike (Exodus 12:23). Therefore, one should always be [enveloped] by a mezuzah….
From where do we know this? From its written form—מְּזוּזֹת (mezuzot), doorposts. Its letters demonstrate: זָז מָוֶת (zaz mavet), Death slinks off, for he is not given permission to attack, and he slinks away from the opening” (Zohar Ḥadash 84d–85a [MhN], cf. Tiqqunei ha-Zohar 25a, 66a).
“Our Rabbis taught: If one rents a house to another, the tenant must provide a mezuzah. But when he leaves, he must not take it with him, except [if he rented] from a gentile, [then] he must remove it when he leaves. And it once happened that a man took it away with him, and he buried his wife and two children” (BT Bava Metsi’a 102a).
“Our Rabbis taught: Children die as a punishment for [unfulfilled] vows….
[However,] Rabbi Me’ir and Rabbi Yehudah disagree: One maintains, It is for the neglect of mezuzah, while the other holds that it is for the neglect of tsitsit. Now, as for the view that it is for the neglect of mezuzah, it is well, as is written, And you shall write them on the מְזוּזוֹת (mezuzot), doorposts, of your house and in your gates, which is followed by, so that your days may be many, and the days of your children (Deuteronomy 11:20). But what is the reason of the view that it is for the neglect of tsitsit?—Rav Kahana, others say Shila Mari: because it is written, Also on your skirts is found the blood of the souls of the poor innocents (Jeremiah 2:34). Rav Naḥman son of Yitsḥaq said, The view that it is for the neglect of mezuzah is also [learnt] from this: Did I not find them tunneling in? (ibid.) [cf. Exodus 22:1: If while tunneling, a thief should be found and is struck down and dies, there is no bloodguilt for him]—they made their entrances like [nothing more than] caves [without doorposts]” (BT Shabbat 32b).