Deuteronômio 11:20 Halacá: Mishneh Torah, Positive Mitzvot, Gray Matter II & Tur

To affix the Mezuzah, as it is said, “And thou shalt write them on the door-posts of thy house” (Deut. 6:9).

Several Responsa serve as precedents for asserting that a man followed his regular routine.³⁰In addition to the sources that we discuss, see Teshuvot Igrot Moshe (E.H. 1:7). Rav Yitzchak Herzog (Teshuvot Heichal Yitzchak, E.H. 2:9:2) considers the possibility of partially relying on a husband’s patterns to determine that a man was at a particular place where a bridge collapsed into the water.³¹Although a pattern is sometimes called a “chazakah,” it is a very different concept than the chazakah that we mentioned earlier, which referred to the assumption that the status quo has been maintained. He notes that the Taz (Yoreh Deah 69:24) rules that if a woman is unsure if she salted a piece of meat before she cooked it, she may assume that she followed her normal pattern of salting the meat. As a precedent, the Taz cites the Gemara’s ruling (Berachot 16a) that if one is reading the Shema and is unsure if he has read the verse of “Uch’tavtam” from the first section of Shema or the second section, the doubt is resolved if he had begun to read the verse of “L’ma’an yirbu,” which follows “Uch’tavtam” in the second section (see Devarim 6:9 and 11:20-21). Since people normally recite Shema in the proper order, a person may assume that he followed his usual routine and proceeded to the next verse of the second section because he had recited everything until then.

The Laws of Mezuzah
It is a positive commandment to write the sections of Shema (Deuteronomy 6:4-9), and of Vehayah Im Shemoa (Deuteronomy 11:13-21), and to affix them upon the doorposts of the entrance, as it is written: And you shall write them on the doorposts of your house and on your gates (Deuteronomy 11:20). And one needs to be very careful with it. It is as the sages, may their memory be blessed, said, "Anyone who has tefillin on his head and on his arm, tzitzit on his garment, and a mezuzah on his entrance is assumed to not sin" (Menachot 43b). That is because the mezuzah has the unification of the Holy One, blessed be He, in it, and he will always remember the unification of the Holy One, blessed be He, in his coming in and in his going out, and place the fear of [God] in front of him so that he will not sin. And anyone careful about it will have his days and the days of his children lengthened, as it is written: In order that your days and the days of your children will be multiplied (Deuteronomy 11:21). But if one is not careful about it, they are shortened. As from the positive [statement], I understand the negative [implication]. And likewise did the sages expound, "For the sin of mezuzah do a person's sons and daughters die when they are young, as it is written: the blood of the souls of the innocent poor (Jeremiah 2:34), and next to it is: you did not find them breaking in [which relates to an improvised entrance lacking a mezuzah]" (Shabbat 32b). And greater than this is that the house is guarded by it, as they expounded on the verse: The Lord is your Guardian, etc. (Psalms 121:8), "A flesh and blood king is inside and his servants protect him from the outside, whereas you sleep in your beds, and the Holy One, blessed be He, guards you from the outside." Hence their placement is on the outer handbreadth, such that all of the house be inside from it and its guarding. Nevertheless, the intention of the one fulfilling it should only be fulfill the commandment of the Creator, may He be exalted, who commanded us about it.