Question: Why is it that on Shabbat night we recite a different text within the “Hashkivenu” blessing and why do we recite “Ve’Shameru Beneh Yisrael Et Ha’Shabbat” afterwards?
Answer: During the weekday Arvit prayers, after “Ga’al Yisrael” blessing, the “Hashkivenu” blessing is recited and it concludes with the words “Shomer Et Amo Yisrael La’ad, Amen.” However, regarding the “Hashkivenu” blessing in the Arvit prayer of Shabbat night, upon reaching the words “Ve’Hagen Ba’adenu,” the following text is inserted: “U’fros Alenu Ve’al Yerushalayim Irach Sukkat Shalom, Baruch Ata Hashem Ha’Pores Sukkat Shalom Alenu Ve’al Kol Amo Yisrael Ve’al Yerushalayim, Amen.”
The Tur (Chapter 268) explains that the reason why the regular text is changed on Shabbat night is because one should not conclude with the words “Shomer Et Amo Yisrael La’ad” (He Who protects the Jewish nation forever), for the Midrash states that on Shabbat, the Jewish nation does not require protection (meaning they do not need to pray for protection), for the Shabbat itself protects. The Yalkut Yosef (Shabbat, page 485), authored by the great Rishon Le’Zion, Hagaon Harav Yitzchak Yosef Shlit”a, quotes that words of Rabbeinu David Abudirhem (page 144), as follows: “One should not conclude “Shomer Et Amo Yisrael La’ad,” for the Midrash states that we do not require protection on Shabbat, for the Shabbat itself protects us. Indeed, the Talmud Yerushalmi (Chapter 4 of Berachot) states explicitly that one should only recite “Shomer Et Amo Yisrael La’ad” on weekdays; however, on Shabbat, one should conclude “U’fros Alenu Sukkat Shalom” and the Geonim write likewise. This is indeed, the custom in several places. Nevertheless, in Seville and Toledo (cities in Spain), the “U’fros Alenu Sukkat Shelomecha” is only recited on holidays, but I do not know why they conclude the blessing this way on holidays and on Shabbat they conclude the blessing as they do on weekdays.”
Similarly, the Kaf Ha’Chaim quotes the holy Zohar which states that the Jewish nation does not require protection on Shabbat; thus, one should conclude the blessing with the aforementioned text on Shabbat. The Sefer Cheshek Shlomo (Chapter 188) states that the reason why this text is used on Shabbatot and holidays is because the words “Sukkat Shelomecha” refer to the Sukkah made from the hide of the Leviathan creature which Hashem shall place the righteous in in the times of the Mashiach at which point all days shall be like Shabbat and holidays for all eternity.
The Shibloeh Ha’Leket (Chapter 65) states that on Shabbat night, one need not request for protection as one would on other weeknights. He proceeds to illustrate this point with a parable: A king once became distanced from his forces until he accidentally entered the boundaries of another country. He was fearful that someone would want to kill him so he made sure to carry around his weapon with him everywhere he went and he was prepared for any situation that may arise. However, when he returned to his own city among his own soldiers, he laid down his personal weapon since his deputies and officers were there to protect him. So too, the Jewish nation is fearful during the rest of the week, for they cannot perform the Mitzvot and delve in Torah study as they should as a result of their various burdens and because of this, they do not have as much of a merit to protect them during the week. We therefore pray that we not be harmed by harmful forces and others who wish to do us evil by reciting “U’shmor Tzetenu U’vo’enu Le’Chaim Tovim Ulshalom” (protect our goings and comings for good life and peace) and then we conclude “Shomer Et Amo Yisrael La’ad,” for this prayer acts as our weapon to protect ourselves. However, when Shabbat arrives and everyone is busy preparing to enjoy Shabbat and to rest on Shabbat, the merit of Shabbat is great for those who remember it by sanctifying it and they need no other protection and thus, requesting peace is sufficient. It is for this reason that “Ve’Shameru Beneh Yisrael Et Ha’Shabbat” is recited in order to teach us that as a result of the Jewish nation’s observance of Shabbat, the Shabbat protects them.