Shtisel 101, Session 22: Kissing the Mezuzah

(4) Hear, O Israel! The LORD is our God, the LORD alone. (5) You shall love the LORD your God with all your heart and with all your soul and with all your might. (6) Take to heart these instructions with which I charge you this day. (7) Impress them upon your children. Recite them when you stay at home and when you are away, when you lie down and when you get up. (8) Bind them as a sign on your hand and let them serve as a symbol on your forehead; (9) inscribe them on the doorposts of your house and on your gates.

§ The Gemara mentions other Romans who converted to Judaism. It relates: Onkelos bar Kelonimos converted to Judaism. The Roman emperor sent a troop [gunda] of Roman soldiers after him to seize Onkelos and bring him to the emperor. Onkelos drew them toward him with verses that he cited and learned with them, and they converted. ...The emperor then sent another troop of soldiers after him, to bring Onkelos, and said to them: Do not converse with him at all. The troops followed this instruction, and took Onkelos with them. 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 the soldiers: What is this? They said to him: You tell us. Onkelos said to them: The standard practice throughout the world is that a king of flesh and blood sits inside his palace, and his servants stand guard, protecting him outside; but with regard to the Holy One, Blessed be He, His servants, the Jewish people, sit inside their homes and He 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.

(13) A person should pay heed to the precept of the Mezuzah; for it is an obligation perpetually binding upon all. Whenever one enters or leaves a home with the Mezuzah on the doorpost, he will be confronted with the Declaration of God's Unity, blessed be His holy name; and will remember the love due to God, and will be aroused from his slumbers and his foolish absorption in temporal vanities. He will realize that nothing endures to all eternity save knowledge of the Ruler of the Universe. This thought will immediately restore him to his right senses and he will walk in the paths of righteousness...

(2) The placement of the mezuzah is in the outer handbreadth of the door.

Rama: There are those who say that when a person leaves his house, he puts his hand on the Mezuzah there and says “God will guard my going, etc.” And so too when one enters a house, one puts his hand on the Mezuzah.

Whenever a person walks out from their door, he should put his hand on the mezuzah and say "Hashem is my keeper Hashem is my protector by my right hand. Hashem will preserve my going out and my coming in from now until eternity."

The basis for placing the hand on the mezuzah is mentioned in the first chapter of Avodah Zarah (11a)