Having informed them (in the previous Pasuk) that the Manna would not fall on Shabbos, why did Moshe repeat it here?
Rashi (citing the Mechilta): He said this to include Yom Kipur and the Yamim Tovim, as the Mechilta interprets - "u'va'Yom ha'Shevi'i" refers to Shabbos; 1 "Lo Yih'yeh Bo" includes Yom-Tov; and "Shabbos" includes Yom Kipur.
See Torah Temimah, note 38.
Rashi (to Bereishis 2:3) writes that Hashem sanctified the Shabbos, in that no Manna would fall. How does this indicate the sanctity of Shabbos?
Maharal (Tif'eres Yisrael, Ch. 40, p. 124): The natural world does not cease to grow or develop on Shabbos, because the material world (Chomer) can never reach a state of rest and completion. The Manna in the desert, however, transcended the natural world; therefore, it rested on Shabbos.
QUESTIONS ON RASHI
Rashi writes: "'And on the seventh day, Shabbos' - 'Shabbos Hu, ha'Man Lo Yihyeh Bo.'" What is Rashi explaining by adding just the term "Hu"?
Gur Aryeh: The Pasuk sounds like Moshe was now giving two directives - a. The seventh day shall be Shabbos; b. There will be no Manna on that day. But Bnei Yisrael already knew that the seventh day is Shabbos! By adding the word "Hu" (it is), Rashi makes it clear that there is only one directive here - 'Today is Shabbos - as you already know - and therefore there will be no Manna today.'
Rashi writes: "The Pasuk comes only to include Yom Kippur and the Yamim Tovim" (i.e., that no Manna will fall on these days). Rashi to Bereishis 2:3, explained that Hashem sanctified the Shabbos in that no Manna would fall. But if no Manna fell on Yom Tov either, in what way is Shabbos more sanctified than Yom Tov?
Gur Aryeh: The Manna did not fall on Yom Tov because it too is referred to as Shabbos. 1 The Kedushas ha'Yom of Shabbos is because it is a Yom Shevisah (cessation of work), and this is what sanctifies all of the Yamim Tovim as well.
Maharal (Gevuros Hashem Ch. 63, p. 285): The blessing of Shabbos was that the Bnei Yisrael gathered one portion of Manna, and then found that it emerged double. 2 Perhaps on Erev Yom Tov this miracle did not occur, and they actually had to manually gather an extra portion for Yom Tov. This may also explain the extra sanctity of Shabbos. 3
Gur Aryeh concludes, citing Mechilta, that the Yamim Tovim were sanctified along with the Shabbos - yet Shabbos is primary. See Rashi to Bereishis 2:2 - The world lacked the concept of Menucha, until Shabbos came; thus, the cessation of work on the Festivals is also by virtue of Shabbos. However, whether the Manna fell on Yom Tov is a matter of dispute among the Rishonim; see Tosfos to Beitzah 2b. (EK)
As above, Maharal implies that this miracle occurred not only the first Erev Shabbos, but every week the Bnei Yisrael were in the desert.
Maharal: It follows that on Shabbos there was no need for the Manna to fall, because the food had already doubled. On Yom Tov, we would need the Manna, and so we had to gather double the previous day. This is a lesser demonstration of Yom Tov's sanctity. See Maharal further, as to whether "Lechem Mishneh" is required at the Yom Tov meals. After all, the miracle that the Manna did not spoil when left overnight, occurred on Yom Tov as well. (EK)