What is the significance of the fact that the Egyptians forced Yisrael to leave?
Why were the Egyptians saying, "Kulanu Meisim"?
Rashi (here and to 12:30): Because the Egyptians were highly promiscuous, and the women would often give birth to many firstborn sons 1 from men who were not their husbands. Consequently, people died (often as many as five or ten in a family) whom they did not know were firstborn. 2
Targum Yonasan: Because when Pharaoh pleaded with Moshe and Aharon to leave, they ignored his request, until Pharaoh and his servants, together with all the people begged Yisrael to leave, because they claimed that if they remained for another moment, all the Egyptians would die. 3
Ibn Ezra (to 5:3): Because Moshe said from the beginning, "Pen Yifga'enu ba'Dever O ve'Charev" (5:3). Now that they saw Dever strike the firstborn, Moshe's words were fulfilled and they all expected to die.
Osher Aharon: First, Hashem sent an angel to afflict all Egyptians with Dever. Then, Hashem Himself - the only One who can distinguish between a firstborn and a Pashut - killed the firstborns.
Maharal (Gevuros Hashem Ch. 52, p. 225): The (non-firstborn) Egyptians continued to die after midnight as well. Refer to 12:31:1.02:1.
See Ramban, who maintains that, according to the simple explanation, the firstborn that died in Egypt were the firstborn from the womb, as indicated by the Mitzvah of Pidyon Bechor. Also refer to 13:2:2:1 and 13:2:2:2.
Moshav Zekenim (to 12:29): Pharaoh was unaware of this; and when Moshe warned about Makas Bechoros, he jeered, 'How many Bechoros are in Egypt - [just] 200?!' (This is astounding. There were multitudes of Egyptians, for each of 600,000 Yisraelim took at least 80 donkeys of gold, silver and clothing from their neighbors! Some say that there were about a billion Egyptians - Refer to 14:7:2:3. Perhaps he holds that Moshe announced Makas Bechoros in advance, and almost all firstborns had already fled Egypt (refer to 11:5:3:4); whereas Moshe told Pharaoh only later (see 10:24:151:4). However, even if Pharaoh thought so, he should have been concerned for himself! - PF) The question arises however, why Moshe did not take precautions to avoid a Chilul Hashem, like he did with regard to 'midnight' (refer to 11:4:1:2)? (Gur Aryeh addresses this, see 12:33:2.1:1.) Also refer to 12:30:2:1.
Ha'Melitz Beinosam: They all expected to die, because, where there was no Bechor, the oldest in the house died. If Bnei Yisrael would remain, the plague would continue, and the oldest in the house would continue to die until they were all dead.
QUESTIONS ON RASHI
Rashi writes: "'We are all dying' - They said, 'It is not as Moshe decreed... Even the regular [sons] are dying, five or ten in one house!'" Why did this happen? Wouldn't the Egyptians be likely to accuse Moshe of inaccuracy?
Gur Aryeh (to 11:5): These additional deaths were not a contradiction to Moshe's prophecy (that all the firstborn would die), but rather in addition to it. Also refer to 11:5:2.1:1 and its note. 1
Gur Aryeh (to 11:5): On the other hand, Rashi (loc. cit.) does see fit to explain another discrepancy (between verses 11:5 and 12:29) as to whether the Makah would extend to the firstborn of the maidservants, or to the firstborn of the captives. These define the scope of the Makah differently, and require explanation.
