(ד) שְׁמַ֖ע יִשְׂרָאֵ֑ל יְהוָ֥ה אֱלֹהֵ֖ינוּ יְהוָ֥ה ׀ אֶחָֽד׃ (ה) וְאָ֣הַבְתָּ֔ אֵ֖ת יְהוָ֣ה אֱלֹהֶ֑יךָ בְּכָל־לְבָבְךָ֥ וּבְכָל־נַפְשְׁךָ֖ וּבְכָל־מְאֹדֶֽךָ׃ (ו) וְהָי֞וּ הַדְּבָרִ֣ים הָאֵ֗לֶּה אֲשֶׁ֨ר אָנֹכִ֧י מְצַוְּךָ֛ הַיּ֖וֹם עַל־לְבָבֶֽךָ׃ (ז) וְשִׁנַּנְתָּ֣ם לְבָנֶ֔יךָ וְדִבַּרְתָּ֖ בָּ֑ם בְּשִׁבְתְּךָ֤ בְּבֵיתֶ֙ךָ֙ וּבְלֶכְתְּךָ֣ בַדֶּ֔רֶךְ וּֽבְשָׁכְבְּךָ֖ וּבְקוּמֶֽךָ׃ (ח) וּקְשַׁרְתָּ֥ם לְא֖וֹת עַל־יָדֶ֑ךָ וְהָי֥וּ לְטֹטָפֹ֖ת בֵּ֥ין עֵינֶֽיךָ׃ (ט) וּכְתַבְתָּ֛ם עַל־מְזוּזֹ֥ת בֵּיתֶ֖ךָ וּבִשְׁעָרֶֽיךָ׃ (ס)
(ד) יש אומרים כשאדם יוצא מן הבית – יניח ידו על המזוזה ויאמר "ה' ישמור צאתי ובואי", וכן כשנכנס לבית. ויש לזה קצת מקור בגמרא פרק "לפני אידיהן" במעשה דאונקלס, עיין שם (עבודה זרה יא א). וכשיוצא לדרך חוץ לעיר, יניח ידו על המזוזה ויאמר: "בשמך טל אטלה", כי "טל" בגימטריא שם כוז"ו הנכתב אחורי המזוזה, שהם אותיות שלאחר שם הוי"ה. ויש מי שכתב שיניח אצבעו השלישי על שם "שדי", ויתפלל לה' שישמרנו בשם זה, וינשק אצבעו זה (ברכי יוסף).
Some say that a person who leaves the house should place their hand on the mezuzah and say: Eternal guard my going out and my coming in." and also when they enter the house. There is a hint at a source for this practice in the Talmud (in the first chapter of Avodah Zarah) in the practice of Onkelos, see there (11a). And when travelling outside the city, they place their hand on the mezuzah and say "in Your Name I will sprinkle dew" since "dew"...There is one opinion that one places the third finger (middle finger) on the name "Shadai," written on the outside of the mezuzah, and prays to God to protect them in this Name, and kisses his finger afterwards (Birkei Yosef-- 18th ce. Jerusalem).
Onkelos bar Kelonimos converted to Judaism. The Roman emperor sent a troop of Roman soldiers after him. He drew them in him with Torah verses; they converted. The emperor then sent another troop of Roman soldiers after him, and said to them: Do not say anything to him, When they were walking, he said: I will say a mere statement to you: A minor official holds a torch before a high official, the high official for a duke, a duke for the governor, the governor for the ruler. Does the ruler hold a torch before the people? They said to him: No. He said to them: But the Holy One holds a torch before the Jewish people, as it is written: “And the Eternal went before them by day in a pillar of cloud, to lead them the way, and by night in a pillar of fire, to give them light” (Exodus 13:21). They all converted. The emperor then sent another troop of soldiers after him, and said to them: Do not converse with him at all. While they grabbed him and were walking, Onkelos saw a mezuza that was placed on the doorway. He placed his hand upon it and said to them: What is this? They said to him: You tell us. He said to them: In the way of the world, a king of flesh and blood sits inside, and his servants guard him outside; but with the Holy One, the servants, sit inside and God guards over them outside. As it is stated: “The Lord shall guard your going out and your coming in, from now and forever” (Psalms 121:8). Upon hearing this, those soldiers also converted to Judaism. After that, the emperor sent no more soldiers after him. §