1) The Sifsei Chachamim on Maseches Berachos says that it must be that the verse is referring to the Jewish people who will be in the future. Since, in the future, Bnei Yisrael will be 600,000, this is also what the verse means now when it calls them Bnei Yisrael.

2) I would like to elaborate on the above. The verse (Shemos 18:4) which lists the sons of Moshe Rabeinu says literally, "and the name of 'the one' was Eliezer." Why does the Torah call Eliezer "one"? It should call him the second son! Rabeinu Bachye there answers that Eliezer is called "one" because he was the source of the great growth of his descendants. He was the father of Rechavyah, who had a great number of offspring. The Torah is telling us that this growth came as a reward for Eliezer's love of unity. He drew everyone together and made them all into "one" family. Eliezer had only one son but he had the Zechus that from that son, Rechavyah, more than 600,000 emerged.

3) Now we may suggest that this love of unity was present only among those who actually left Mitzrayim. A lot of the Bnei Yisrael who did not leave did not actually want to leave because they felt comfortable there. They were lacking the feeling of unity with their brethren. These were not the genuine Bnei Yisrael who merited leaving Egypt.

Chag Kasher v'Same'ach,

Dovid Bloom

1) I posed your question to a Talmid Chacham and he gave quite a different answer. He said that when Chazal make a Derashah, they may do so only on an explicit verse; they cannot make a Derashah on another Derashah.

2) I will try to explain this idea. The Derashah that the Gemara makes in Berachos (end of 7a) is a Gezeirah Shavah (which is one of the 13 principles by which the Torah is expounded). The way we know that only one-fifth of Bnei Yisrael left Egypt is also through a Derashah; Shemos 13:18 says that Bnei Yisrael went up "Chamushim" from Mitzrayim. Literally, this means "armed," but Rashi there cites an interpretation that only one out of "Chamesh" -- five -- left Egypt.

3) The teaching about "one-fifth" is not the Peshat, the simple reading. It itself is derived from a Derashah. One cannot fit the Derashah of "Revi'a Revi'a" onto the other Derashah of "Chamesh." When Chazal make a Derashah they have the power to do so only on an explicit verse, but not to put their Derashah onto another Derashah of Chazal.

4) In addition, I must apologize for misquoting the Sifsei Chachamim in my previous reply. The Sifsei Chachamim asks a slightly different question than yours, Elisha. He asks that when the verse that the Gemara cites (about Yisrael multiplying) was stated, they were not yet 600,000. They became 600,000 only when they left Egypt, so how can the Gemara learn 600,000 from a mentioned earlier? The Sifsei Chachamim answers that this verse was said according to what they were going to be at the end, namely 600,000.

5) So while I got the question of the Sifsei Chachamim wrong, I think I at least got the answer right!

Elisha, thank you very much for your timely question making us think about Yetzi'as Mitzrayim. May we be Zocheh to a Ge'ulah Sheleimah!

Dovid Bloom

The Talmid Chacham who gave the above answer also showed me a source for his answer. Rashi (Shabbos 132a, end of DH Akiva) writes, "Torah she'Ba'al Peh cannot be expounded through the Thirteen Principles." According to this, one can argue that it is not possible to use a Gezeirah Shavah here in Berachos 7a. The teaching that only one out of five left Egypt is not written explicilty in the Torah. It should therefore be considered part of the Oral Law. If so, one cannot use a Gezeirah Shavah on this teaching, because Rashi tells us that a Gezeirah Shavah can be used only for something stated explicitly in the Torah.

Dovid Bloom