Seeing as Moshe just said that he would never see Pharaoh again (10:29), and Hashem never spoke to Moshe in Pharaoh's palace (see Rashi to 9:21 and to 12:1), when did Hashem say this to Moshe?
Rashi (to 11:4) and Ramban: On this occasion, Hashem went against His principles and spoke to Moshe in Pharaoh's palace, before Moshe left. 1
Riva and Moshav Zekenim: Hashem told Moshe already in Parshas Shemos, to tell Pharaoh "Anochi Horeg Es Bincha, Bechorecha" (4:22). 2
Refer to 11:1:151:3.
Tosfos ha'Shalem (to 11:4, #3, citing Riva): Hashem did not tell Moshe. Moshe issued this statement on his own, and "When a Tzadik decrees, Hashem fulfills." 3
To conform to Moshe's statement that he would not see Pharaoh again - and 'when a Tzadik decrees, Hashem carries out' (See Shabbos 59b).
Hadar Zekenim: Since Pharaoh was warned then, Moshe did not warn now about Makas Bechoros. (Why does he say that there was no warning now? "v'Yardu Kol Avadecha... " (11:8) proves that the Parshah was said in front of Pharaoh! - PF)
Riva: Hashem said only "v'Avarti... ba'Laylah" (12:12). Moshe added 'midnight;' and Hashem carried it out so that Moshe should not appear to be a liar.
What are the implications of the word "k'Shalecho"?
Seforno: He meant that, just as Pharaoh expelled Moshe and Aharon from his presence, 1 so too, would he expel Yisrael from the land.
Even though grammatically, it ought to have said 'k'Shalech'chem."
What is the significance of the fact that Pharaoh will expel all of Yisrael from Egypt ?
Seforno: Because that is the way that Hashem acts (Midah K'Neged Midah) towards those who refuse to submit to His will. He forces them to do what He wants in a painful way, against their wishes. 1
As The Pasuk says, " ... Because you did not serve Hashem your G-d with joy ... So you will serve your enemies" (Devarim 28:48-49). See also Bamidbar 14:28); and as Chazal say in Pirkei Avos 4:10), 'Whoever negates the Torah when he is wealthy, will eventually negate it when he is poor.'
What are the implications of the (otherwise superfluous) word "Kalah Garesh Yegaresh Eschem"?
Rashi and Seforno: It implies that Pharaoh will send out all of Yisrael (men, women, children, and animals - Oznayim la'Torah) - as opposed to the previous two occasions when Pharaoh only drove out Moshe and Aharon. 1
See also Keli Yakar.
Why the doubled expression, "Garesh Yegaresh?" Also see the doubled term at the end of Parshas Shemos, "Yeshalechem... Yegareshem" (6:1)?
Refer to 6:1:153.
QUESTIONS ON RASHI
Rashi writes: "'Kalah' - 'Gemira; Kalil' (i.e. completely)." What is Rashi trying to explain with these terms?
Gur Aryeh: First, Rashi brings the Targum, who translates "Kalah" with the term "Gemira" - "completely." As proof that this is a correct translation, Rashi points out that "Kalah" and "Kalil" have the same root, and we know that "Kalil" also means "completely" (as in Vayikra 6:15).
Rashi writes: "'Kalah' - ... completely; he will send away all of you." Why does this need to be added?
Gur Aryeh: "Kalah" means completely (see 11:1:4.1:1). But in this context, it cannot mean "he will send you away absolutely" with no plans to take you back; for in fact, Pharaoh still expected them to return after three days! Rather, it will be complete in the sense that no one will be left behind.
Rashi writes (to 11:4) that this Parshah was said to [Moshe] in Pharaoh's palace. But later, Rashi (to 12:1) cites a Mechilta that even a simple Tefilah was not said in the city due to its idols, and all the more so a severe Dibur?
Moshav Zekenim #1: The palace was inappropriate for Tefilah or for giving a Mitzvah, but was appropriate for discussing a plague.
Moshav Zekenim #2: Moshe left the city in order to see the hail in the fields; not because he could not Daven in the city. 1
Moshav Zekenim #3, Riva (to 11:4), Da'as Zekenim and Hadar Zekenim (citing a Midrash): Hashem lifted Moshe ten Tefachim (above the ground) due to the Tum'ah of the idolatry in Egypt. 2
Moshav Zekenim #4: Rashi means that Parshas 3 Makas Bechoros was said to Pharaoh before Moshe left him, but Hashem had told it to Moshe earlier (refer to 11:1:1:2).
Refer to 11:1:1:4.
Moshav Zekenim: This is unlike the Mechilta, which makes a Kal va'Chomer!
Moshav Zekenim: If so, how does the Mechilta prove that Parshas ha'Chodesh was said outside the city? Perhaps Hashem lifted Moshe ten Tefachim!
His text of Rashi said 'was said to him this Parshah.' Most commentaries cite Rashi as saying only, 'was said to him.' However, most texts of Rashi say 'this Nevu'ah was said to him' (like Shemos Rabah 18:1). If so, it is difficult to explain ''was said to Pharaoh this Nevu'ah [via Moshe]." (PF)