What is the significance of the word "Koh" in this Pasuk? It will be repeated at the beginning of the next Pasuk, "Koh Amar Hashem" (7:17)?
Rashi: Besides the simple meaning of the Pasuk (that Pharaoh has not listened up to the present), it also insinuates that Pharaoh will not listen until Makas Bechoros, which will be introduced with "Koh Amar Hashem" (11:4). 1
Ramban: The Pasuk simply means that because Pharaoh did not listen until now (where he was merely shown signs), the era of Makos was about to begin - and he had only himself to blame.
Sifsei Chachamim: But that phrase appears before numerous Makos? Refer to 7:16:1.3:1.
QUESTIONS ON RASHI
Rashi writes: "Ad Koh (lit. until now) - ... In the Midrashic sense, [you will not obey,] until you hear about Makas Bechoros, which I will introduce with [the word] Koh -- 'Koh Amar Hashem, at about midnight, etc.' (11:4)." Why will the topic of Makas Bechoros open with this word, "Koh"?
Gur Aryeh: Makas Bechoros is the end-goal of all the Makos; it would cause the Bnei Yisrael to go free. The word "Koh" always refers to a specifically-defined subject. When one reaches the end of a process, one must act in the precise way that will bring about the desired goal.
Rashi writes: "[... You will not obey] until you hear about Makas Bechoros, which I will introduce with [the word] Koh." How then should we learn our Pasuk, according to this interpretation?
Gur Aryeh: Moshe hinted to Pharaoh that the Makos would extend until "Koh" (i.e. Makas Bechoros), but no further. 1 Afterwards, Pharaoh would realize that Moshe's words came true.
Gur Aryeh: The Midrash comes to interpret why the phrase "Ad Koh" is used, rather than 'Ad Atah.'
Rashi writes: "[... You will not obey] until you hear about Makas Bechoros, which I will introduce with [the word] Koh." But many of the Makos open with the word "Koh"!
Gur Aryeh: In the other instances, the word Koh is not referring to the Makah itself, but to preliminary statements; such as "Koh Amar Hashem, send out My nation, and they shall serve Me!" (7:26). Only regarding Makas Bechoros does the word "Koh" introduce the Makah itself.
Rashi writes: "... Until Makas Bechoros, which I will introduce with [the word] Koh." What is the significance of the expression "Koh Amar Hashem"?
Gur Aryeh (to Bamidbar 30:2): Chazal teach that all subsequent Nevi'im would prophesy with the words 'Koh Amar Hashem,' yet only Moshe used also the phrase "Zeh ha'Davar." This is because Moshe 'prophesied through a clear lens' (Yevamos 49b; Mizrachi loc. cit). Nonetheless, sometimes even Moshe said 'Koh Amar Hashem' (e.g., before Makas Bechoros)! Gur Aryeh explains that the Torah's Halachos were transmitted with "Zeh ha'Davar," for the Mitzvos are Hashem's eternal and unchanging will; this aspect of prophecy was unique to Moshe. At other times, Moshe prophesied about specific things Hashem would do or command, which were of a timely nature, rather than eternal. For these, the term 'Koh' is appropriate.
