- Using היכר ציר to determine the direction of a doorway
Shmuel said: במזוזה הלך אחר היכר ציר – regarding the laws of mezuzah, follow the indication of the pivot. Rav Adda explained that this refers to the hole in the ground in which the pin of the door is inserted, on which the door turns. The Gemara illustrates when we follow this indicator: כגון פיתחא דבין תרי בתי – in the case of the entrance between two houses, בין בי גברי לבי נשי – between the men’s house and the women’s house. Rashi explains that someone divided his home in two, one side for men visiting his house, and the other for the women of the house to conduct their activities privately, and a doorway opened from one to the other. Since the mezuzah must be placed on the right side of the entrance, we must determine which direction is the entry. Here, Shmuel ruled that whichever room the pivot is in is considered the “inside,” and the mezuzah is placed on the right side for entering that room.
- The proper height for placing a mezuzah
Shmuel said: מצוה להניחה בתחלת שליש העליון – it is a mitzvah to place [the mezuzah] at the beginning of the upper third of the doorpost (i.e., just above two-thirds of the doorpost’s height). Rav Huna says one must raise it above a tefach from the ground, and distance it a tefach from the beam over the door, and the rest of the entrance is fit for the mezuzah. In a Baraisa, Rebbe Yehudah says exactly like Rav Huna, and Rebbe Yose says that "וקשרתם" – and you shall bind them (tefillin) is written near "וכתבתם" – and you shall write them (מזוזות) to teach: מה קשירה בגובה – just as binding (תפילין של ראש) is at the top of one’s head, אף כתיבה בגובה – so too is the writing (the mezuzah) placed at the top of the doorpost. Since Rebbe Yose seems to hold the mezuzah is placed at the very top, neither Tanna holds like Shmuel!? The Gemara answers that Shmuel holds like Rebbe Yose, and his statement was regarding להרחיקה – distancing it from the upper beam, teaching that one should not distance it from the upper beam more than a third, but it can be higher.
- Placing the mezuzah near רשות הרבים, Hashem guards His servants from outside
Rava said: מצוה להניחה בטפח הסמוך לרה"ר – it is a mitzvah to place [the mezuzah] within the tefach closest to the public street. The Rabbis explain: כדי שיפגע [במצוה] מיד – so that he should encounter the mitzvah immediately as he enters the doorway. Rav Chanina of Sura explains: כי היכי דתינטריה – so [the mezuzah] will guard [the house] from מזיקין from the very beginning of the entranceway. Rebbe Chanina said: בוא וראה שלא כמדת הקדוש ברוך הוא מדת בשר ודם – Come and see that Hashem’s trait is not like a flesh-and-blood [king’s] trait. Regarding a בשר ודם, מלך יושב מבפנים ועם משמרין אותו מבחוץ – the king sits inside his palace, and his subjects guard him from outside. But Hashem is not like that; rather, עבדיו יושבין מבפנים והוא משמרן מבחוץ – His servants sit inside their homes and He guards them from outside, as the passuk says: ה' שמרך ה' צלך על יד ימינך – Hashem is your Guardian, Hashem is your shade at your right hand.