Why did Moshe have to leave the town in order to pray to Hashem?
Rashi and Ramban #1 (citing the Mechilta): Because the town was full of idols. 1
Ramban #2: Because, whereas Moshe generally prayed in his home; this time, to counter the affects of the plague, he wanted to raise his hands heavenwards for the thunder and hail to stop, and it would not have been appropriate to do so in town.
Riva: This Makah was in the field. Moshe wanted to see the damage to the trees, and then Daven for it to end.
Oznayim la'Torah (citing the Ma'aseh Hashem): Because since the plague took place in the field, it was appropriate to Daven there.
Sifsei Chachamim: Because the Egyptians' idols (the sheep, which they worshipped) were generally kept in the fields, and it was only now, when the G-d-fearing among them gathered the sheep into their houses, that Moshe needed to leave the town to Daven. 2
Also the Da'as Zekenim says this, but he concludes that 'we learn from here that all Moshe's Tefilos were said outside the town.' (Perhaps there was always idolatry in the town, and the Torah mentions it now, when it was full of idolatry, so that we should know the reason (PF))
Why did Moshe find it necessary to inform Pharaoh that he would Daven when he left the precincts of the town?
Ramban: Because, as opposed to the previous occasions, when Pharaoh asked for the plague to be removed only the next day, Moshe did not need to inform Pharaoh where he would Daven; this time he asked for the hail to cease immediately, 1 and Moshe was obligated to tell him that he would only Daven as soon as he left the precincts of the town. 2
Sifsei Chachamim: Refer to 9:29:1:5.
Riva: Refer to 9:29:1:3.
What is the significance of Hashem's words, "Lema'an Teida Ki La'Shem ha'Aretz!"? How would the end of the Makah teach Pharaoh this lesson?
Ramban: Refer to 8:18:2:1*.
Seforno: He said this with reference to the fact that, thunder and hail would (miraculously) cease simultaneously - from one moment to the next. 1
Maharal (Gevuros Hashem, end Ch. 32, p. 124): Moshe set a specific moment for the Makah to end (i.e., "as I leave the city"), which Hashem would now fulfill. This would be a revelation of His Unique Name. 2
Seforno: To emphasize the fact that the cessation of the plague was not because Hashem thought that Pharaoh had done Teshuvah - as the next Pasuk (9:30) clarifies.
Nature does not operate 'on demand' at a specific moment! This event would therefore show Hashem's Oneness (refer also to 7:26:152:1). Maharal adds that whereas in Makas Tzefarde'a, Moshe invokes the Name of Hashem during the warning prior to the Makah - because the time of its removal would be decided by Pharaoh; here in Barad, Moshe is informing him when the Makah would end, so He invokes Hashem's Name at this time. (Also see 7:17:1.1:1 (Makas Dam), 8:16:1:1 (Arov), and 11:4:152:1 (Makas Bechoros). (EK)
