The Gemara answers that the Mishnah is only referring to two cases, Besulos
and Be'ulos. It means to say that both Besulos and Be'ulos *i.e.* women who
became widows from either Erusin or Nesu'in, must wait three months.
(a) Why does the Gemara assume, in its question, that if the woman is a
Besulah she must have only had Erusin with her previous husband? It is also
possible for a woman to be a Besulah from Nesu'in (in a case where the
husband did not live with her after the Chupah)! Why, then, does the Gemara
assume that a woman can only be a Besulah if she fell to Yibum *from
Erusin*? (ARUCH LA'NER)
(b) Also, the Gemara's answer that the terms "Arusos and Nesu'os" in the
Mishnah are *explaining* the earlier terms, "Besulos and Be'ulos," is not
clear. Why did the Mishnah have to explain "Besulos and Be'ulos?" By saying
"Besulos," it must be referring to a woman who was only an Arusah, as the
Gemara asked in its question, so why does the Mishnah have to explain it if
it is something so obvious?
(a) The Gemara understood that even if "Besulos" refers to a Nesu'ah who,
after the Chupah, did not live with her husband, the wording of the Mishnah
is still problematic, because then there would be no point in the Mishnah
mentioning "Besulos" and "Be'ulos" at all. It should have just said "Arusos
and Nesu'os have to wait three months," and all of the women would have been
included.
The Gemara answers its question by saying that the terms "Arusos and
Nesu'os" are explaining the terms "Besulos and Be'ulos." The Mishnah wants
to explain that the term "Besulos" means that she was only an Arusah from
her first husband. If she became a Nesu'ah (through Chupah) but did not yet
have relations, then she is *not* called a Besulah. Rather, she is in the
category of a Be'ulah, even though she never had relations.
What is the point of emphasizing this? What difference does it make, if all
women must wait three months in any case? The answer is that it makes a
difference according to Rebbi Yosi and Rebbi Yehudah, who say that an Arusah
(i.e. a Besulah) does *not* need to wait three months. They will agree that
if she became a Nesu'ah (through Chupah) and did not have relations, she is
considered a Be'ulah and must wait three months. (M. Kornfeld)
(b) The MAHARSHA says that RASHI in Eruvin (47a, DH Achas Besulos) explains
the answer of our Gemara in a different way. According to the way the
Maharsha understands Rashi there, the Gemara is answering as follows: The
Mishnah is saying that they must wait three months after their second
husband died, whether they were Besulos or Be'ulos when they married their
first husband (who died or divorced them). The Mishnah goes on and says that
they must wait three months whether their *second* husband died (or divorced
them) after Erusin, or after Nisu'in.
This explanation has the advantage that it fits more smoothly with the words
of our Gemara (because according to the first way of explaining the Gemara,
the Gemara should have said that the second part of the Mishnah "is
explaining" the first part -- "Perushei Ka Mefaresh"). However, according to
this explanation, what does her status from her *first* husband have to do
with whether or not she must wait three months after the passing of her
*second* husband? If she was an Arusah from the second marriage (with the
man who died now), then what difference does it make if she was a Be'ulah
from the first marriage? That is inconsequential to her status now (i.e. she
is certainly not pregnant from her first husband!). (NEHOR SHRAGA)
The answer might be as follows. Had the Mishnah just mentioned Arusos who
were *Be'ulos* from the previous marriage, we would have thought that only
they have to wait three months, as a Gezeirah, because people know that they
had Nisu'in with one husband and might confuse the second husband with the
first. The Mishnah teaches that even if a woman was a Besulah from both
*marriages*, even from the first, she still has to wait three months.