What did Moshe mean when he said to Pharaoh, "Hispa'er Alai"?
Rashi, Targum Onkelos and Targum Yonasan: He was issuing Pharaoh a challenge ('Pride yourself; boast over me') - to ask Moshe to do something that he would not be able to achieve. 1
Rashbam: He was telling Pharaoh that he would carry out his request, irrespective of how big (i.e. difficult) it would be. 2
Oznayim la'Torah: He gave Pharaoh three proofs that the plagues were not based on witchcraft - a. That he would remove them at any time that Pharaoh chose; 3 b. That they wold be removed in the order that he predicted - 'from Pharaoh, from his servants and from the people; c. That they would remain in the River Nile.
Rashi to Devarim 4:34: And it is trials such as this that the Torah refers to as "Masos."
Rashbam: Like the Pasuk in Shoftim 7:2.
Unlike witchcraft which disappears automatically when its time runs out.
What did Moshe mean when he said, "l'Masai A'tir Lecha... "? Why the extra 'Lamed'?
Rashi: Moshe was asking Pharaoh (not when he wanted him to Daven - which he would do immediately - but rather) when he wanted the plague to be removed.
Ramban: As a matter of principle, the moment Moshe Davened to Hashem, the plague came to an abrupt end, and the extra 'Lamed' is not significant. 1
Rashbam: Since the frogs were unlikely to all die in one go, he was asking him by when he wanted all the frogs to have died.
Seforno: As opposed to the witchcraft of the magicians, which lasts only for a limited time and then disintegrates, Hashem's miracles are not limited to a time-period. Consequently, Moshe told Pharaoh that he should fix a final date for the plague and Hashem would comply. 2
Hadar Zekenim, and Riva (to 8:6): There is a Pesik (a break) between "l'Masai" and "A'tir." Moshe asked, 'When will you send out Yisrael? [If so,] I will pray for you now.'
Ramban: As we often find - See for example Shemos 8:19; and Devarim 9:7.
Seforno: Moreover, unlike witchcraft, the frogs would not simply disappear, but would remain in the river - as the Pasuk states in 8:7.
Rashi (to 7:25) cites Chazal, that each Makah remained in force for a quarter of a month. If that term had already elapsed, why did Moshe have to pray for it to be removed? If the time had not yet passed, then the Makah would not last for its full duration!
Gur Aryeh, Maharal: Refer to 7:25:1.3.
What message is Hashem conveying to Pharaoh in the latter half of the Pasuk?
Ramban: He was informing Pharaoh that He would destroy the frogs from the land, and that he need not fear their return, even though some would remain in the Nile. This would impress upon him that the plague was sent by Hashem, solely for the sake of Yisrael. 1
As the next Pasuk concludes, "So that you should know that there is no-one like Hashem our G-d!" (8:6).
QUESTIONS ON RASHI
Rashi writes: "L'Masai A'tir Lecha' (for when shall I pray for you) - ... For when do you want that [the frogs] should die?" Why does Moshe need to word it in this way, rather than just saying 'Masai' (when)?
Gur Aryeh #1: Rashi explains that Moshe emphasized that he would pray today, that the frogs would die later, at the appointed time. This would be a more difficult feat (than if they were to die immediately upon Moshe's praying). 1
Gur Aryeh #2: (Explaining unlike Rashi,) it is because the term 'Masai' does not always mean a set time. Sometimes it conveys astonishment; as in, 'When, O when will this actually happen?' 2 "L'Masai," on the other hand, always means a set time.
Gur Aryeh: Moshe would have to pray for two things - a) That the frogs should die; b) that this should take place at the designated time.
Gur Aryeh: For example, the word "Masai" in the verse, "When will I [once again] come and appear before G-d?" (Tehilim 42:3).
Rashi writes: "[The term] 'A'tir' [is like] 'Ha'tiru' (8:4) and 'v'Ha'tarti' (8:25) ... all of these expressions with root Ayin-Tav -Reish mean 'to increase supplication.'" What does Rashi mean?
Gur Aryeh: The verb for increase (l'Harbos) always comes in causative (Hif'il) form - i.e. causing an increase in something else. Therefore, verbs like "A'tir" also come in Hif'il form; meaning, "I shall cause [my] supplication to be increased." 1
Gur Aryeh: When this verb does appear in Kal form - "va'Ye'tar" (8:26), Rashi in fact explains differently - "he exerted himself in prayer" (Rashi to 8:26).
