(טו) וְהִנֵּ֨ה אָנֹכִ֜י עִמָּ֗ךְ וּשְׁמַרְתִּ֙יךָ֙ בְּכֹ֣ל אֲשֶׁר־תֵּלֵ֔ךְ וַהֲשִׁ֣בֹתִ֔יךָ אֶל־הָאֲדָמָ֖ה הַזֹּ֑את כִּ֚י לֹ֣א אֶֽעֱזָבְךָ֔ עַ֚ד אֲשֶׁ֣ר אִם־עָשִׂ֔יתִי אֵ֥ת אֲשֶׁר־דִּבַּ֖רְתִּי לָֽךְ׃ (א) אנכי עמך. לְפִי שֶׁהָיָה יָרֵא מֵעֵשָׂו וּמִלָּבָן:
(15) Remember, I am with you: I will protect you wherever you go and will bring you back to this land. I will not leave you until I have done what I have promised you.”Rashi:אנכי עמך I AM WITH THEE — God promised him this because he was in terror of Esau and Laban.
בבא בתרא ז:ב
כופין אותו לבנות לעיר כו': (ת"ר כופין אותו לעשות לעיר דלתים ובריח) ורבן שמעון בן גמליאל אומר לא כל העיירות ראויות לחומה אלא עיר הסמוכה לספר ראויה לחומה ושאינה סמוכה לספר אינה ראויה לחומה ורבנן זימנין דמקרו ואתי גייסא
Bava Batra 7b
The mishna teaches that the residents of a city can compel each inhabitant of that city to contribute to the building of a wall, double doors, and a crossbar for the city. The Sages taught in a baraita: The residents of a city can compel each inhabitant of that city to build double doors and a crossbar for the city. And Rabban Shimon ben Gamliel says: Not all cities require a wall. Rather, a city that adjoins the state border requires a wall, whereas a city that does not adjoin the state border does not require a wall.The Gemara asks: And why don’t the Rabbis make this distinction? The Gemara answers: Even if a city does not adjoin the border, it sometimes happens that invading troops come into the area. Therefore, it is always good for a city to be protected by a wall.
The Gemara discusses the division of expenses among travelers in a caravan. The Sages taught in a baraita: In the case of a caravan that was traveling in the desert and a troop of bandits stood over it in order to attack and pillage it, and the members of the caravan agreed to pay ransom to the bandits, they calculate each traveler’s contribution according to the amount of money he is carrying, and they do not calculate according to the number of souls in the caravan, i.e., the expense is not divided equally among the travelers.
(ג) שומרי העיר ששומרין בעצמן בלילות ונתפשרו עם המושל לתת קצבה לשנה גובין לפי ממון אע"פ שמתחלה הוצרכו לשמור בשוה (מרדכי פ"ק דב"ב) ודוקא בכה"ג אבל אם העכו"ם עדיין שומרים והיהודים שוכרים שנים או שלשה לשמור במקומן עדיין אקרקפתא דגברא מונח וגובין בשוה הן דל הן עשיר
Guardians of the city who guard themselves and agree with the ruler to give a fixed amount per year, collect according to the financial ability of the residents even though they have to guard equally. (the Mordechai)
And specifically in this case but if non Jews are guarding and Jews are hiring two or three to guard in their place, then it falls on the heads of the residents (i.e. the number in each family - and a family with more people will have to pay more) whether they are poor or rich
תוספות פסחים מו: ד"ה רבה אמר
ואם תאמר אי אמרינן הואיל א"כ בטלת כל מלאכת שבת הואיל וראוי לחולה שיש בו סכנה וי"ל כיון דלא שכיח כלל לא אמרינן הואיל
Tosafot: Pesachim 46:
And if you will ask, perhaps since, if you cook, this food can be used for a patient whose life is in danger, this is too remote and indirect to say such a thing.
- R. Akiva Eger (1761-1837) writes that when the risk is one in a thousand, it is not considered pikuach nefesh.
- R. Ya'akov Etlinger (1798-1871) writes that when there is no choleh l'faneinu, it is not considered pikuach nefesh.
- R. Avraham Yeshaya Karelitz (Chazon Ish 1878-1953) states that the real criterion is whether it is a situation where we would gather in prayer as a response to the situation.
- R. Moshe Feinstein (1895-1986) presents a similar idea. He suggests that it depends on the person. Some people are very nervous and they may violate Shabbos in certain situations where more relaxed individuals may not.
- R. Shlomo Zalman Auerbach (1910-1995) gives a practical litmus test: If this situation occurred during the week and one would act with great alacrity and nervousness, it is considered pikuach nefesh. If not, it is not considered pikuach nefesh.