Why was Moshe unable to keep his hands aloft?
Rashi #1: It was a punishment for being lax in the Mitzvah - by sending Yehoshua to war to lead the troops, and not going himself. 1
Rashi #2 (citing Berachos 54b) and Ramban #1: Because he was physically unable to do so without support.
Ramban #2 (citing the Midrash): Because it is forbidden to stand with hands raised for three hours.
Targum Yonasan: It was a punishment for delaying the battle for the next day, and not engaging in the defense of Yisrael immediately. 2
But Rashi (to Shmuel I 30:17) explains that there too, when David fought with Amalek, he only succeeded in defeating them "l'Macharasam" - because it is the way of Amalek to be defeated "Machar" - as we find here. (For Maharal's commentary, see above, 17:9:5.2:1 .)
Why did they take a stone for Moshe to sit on, and not a cushion or something softer?
Rashi and Targum Yonasan: Since Yisrael were suffering, Moshe made a point of suffering together with them. 1
Ta'anis 11a: And we learn from here that even a complete Tzadik should commiserate with the community in their suffering. See Torah Temimah, note 10.
What are the connotations of the word "Emunah" in this Pasuk?
Rashi and Targum Yonasan: It refers to Moshe's Tefilah, which he prayed with deep Emunah, hands outstretched. 1
Ramban #1: It means that his hands did not sag but remained firmly aloft without letting up until sunset. 2
Ramban #2 (according to Kabalah): Moshe's ten extended fingers pointed heavenwards hinted at the ten Sefiros 3 - clinging to the Emunah that was fighting on behalf of Yisrael. 4
Ramban: Like we find for example, in Nechemyah 11:23, 10:11; and in Yeshayah 22:23 .
Malchus, Yesod, Hod, Netzach, Tif'eres, Gevurah, Chesed, Chochmah, Binah, Da'as.
Ramban: This is a similar concept to that of the Kohanim, who stretch out their hands when they Duchen (recite Birkas Kohanim). See also Ba'al ha'Turim, who explains that "Emunah" refers to the merit of Avraham; "Ad Bo," to the merit of Yitzchak; and "ha'Shemesh," to the merit of Yaakov.
What is the significance of sunset here?
Rashi: Because the Amalekim were practiced astrologers, 1 who could assess the time that they would win by reading the stars. So Moshe stopped the sun in its tracks to confuse them.
Mechilta: To teach us that Bnei Yisrael were fasting - and that they were obligated to continue until nightfall.
QUESTIONS ON RASHI
Rashi writes: "Moshe remained, his hands faithfully spread towards Heaven, in reliable and prepared Tefilah (Tefilah Ne'emanah u'Nechonah)." Why is spreading of the hands associated with Tefilah?
Maharal (Chidushei Agados Vol. 3, p. 42, to Bava Metzia 85b): Indeed, we learn this from Moshe Rabeinu. That is why one must clean and sanctify his hands prior to Tefilah. 1
Maharal (Nesivos Olam, Nesiv ha'Avodah Ch. 16, p. 127) discusses the Mitzvah of Netilas Yadayim prior to meals. He cites the Gemara, "One who is lax about Netilas Yadayim will be uprooted from the world" (Sotah 4b) - because the hands are the start of a person (e.g. if he extends them outwards, past his head). A new beginning follows immediately upon a state of lacking (He'eder) - which can attach itself to the hands. Similarly, the Kohanim must wash their hands prior to the Avodah (see Maharal as to why the Kohanim must wash their feet as well.) From this, we may derive that the idea in raising one's hands in prayer, is to connect a person to his roots - which are above. (EK)
Rashi writes: "'Until the sun set' - Because Amalek calculated the hours in astrology, [to determine] what hour they could be victorious; Moshe made the sun stand still on them, mixing up the hours." What do we learn from this miracle, in terms of the progression of the miracles involved in the Exodus?
Maharal (Gevuros Hashem Ch. 34, p. 128): The Ten Makos in Egypt each attacked one specific (Prati) aspect 1 of Egypt. In the aftermath of Makas Bechoros, Pharaoh understood that Yisrael has a G-d, and that therefore Yisrael would no longer be under his control. Yet Pharaoh still thought of E-lokei Yisrael as a specific power; and he therefore thought that he might still be able to defeat Yisrael under the right circumstances - and so he led Mitzrayim in chasing after them. Only as Mitzrayim drowned in the sea, which is "encompassing" in essence, did they learn that Hashem's might is all-encompassing. 2 Yet Bnei Yisrael still believed that Hashem's power was limited to the lower realms. Now, during the war against Amalek, Hashem halted the sun, thus they learned that He rules over the heavens as well. At Matan Torah, they learned that Hashem rules even above the heavens; and that there is none other. 3
For our discussion regarding the order of the Eser Makos, and what lesson was demonstrated by each one (and then ultimately by Keri'as Yam Suf), see our commentary to Shemos 7:14 ; specifically 7:14:4:1 .
For example, some of the plagues in Egypt stuck the Nile - a specific body of water; whereas at Keri'as Yam Suf, the sea itself was split - and all of the world's seas are one. The Makos are referred to as "Etzba Elokim" (8:15)); whereas Keri'as Yam Suf was an encompassing Makah called "ha'Yad ha'Gedolah" (14:31). Also see our comments to Pasuk 14:16 above.
Also see Maharal (Gevuros Hashem, end Ch. 42, p. 160) - According to one opinion in the Gemara (Zevachim 116a), Yisro was inspired to join Klal Yisrael due to what he heard about the war against Amalek. Geirus, attachment to Yisrael, comes about when their great level is evident to all; whereas as long as Amalek stands in opposition to Yisrael, they impede the revelation of their stature. It was only when Yisrael overpowered the enemy - and remained in a state of unity - that Yisro came and converted.