(a) The RITVA says that the words of the Tosefta are in error. Our Gemara
says clearly that women are obligated in the Mitzvah, and thus they can be
Motzi men. This is also the view of RASHI (Erchin 3a, DH la'Asuyei), who
rules that a woman may read for a man. This implies that a woman's obligation
is the same as a man's.
(b) TOSFOS in Sukah (38a, DH b'Emes Amru), citing the BEHAG, says that women
are not able to be Motzi a *Tzibur* (a large group) of men because of Kavod
ha'Tzibur (it is a lack of Tzniyus). However, a women is able to be Motzi an
individual man alone.
(c) TOSFOS here (DH Nashim, and in Erchin 3a, DH la'Asuyei) understand the
Behag differently. He says that the BEHAG means to say that women can only be
Motzi other women, but not men. What, then, is the point of telling us that
they are obligated in the Mitzvah? The Chidush is that women only have an
obligation to *hear* the Megilah, and not to *read* it. We might have thought
that they need someone who is also obligated to *read* the Megilah to be
Motzi them. Therefore, the Gemara teaches that they fulfill their obligation
by hearing the Megilah read by another woman. Men, on the other hand, are
obligated to *read* the Megilah, and therefore women cannot be Motzi men.
What is the logic behind the separate nature of the obligation for women and
The MARCHESHES (Hagaon Rav Henoch Eigis of Vilna, may Hashem avenge his
death), explains that the reading of the Megilah is made up of two
components: (1) reading as a Zechirah (verbal declaration of remembrance) of
Mechiyas Amalek (see Megilah 18a; the Avnei Nezer also infers this from a
Yerushalmi). (2) Pirsumei Nisa (publicizing the miracle of Purim). The
Marcheshes explains that a woman is obligated only in the component of
Pirsumei Nisa, since they were part of the miracle of Purim; a woman is not
obligated to read the Megilah in order to fulfill Mechiyas Amalek, because
only one who is obligated to go out to war against Amalek is obligated in the
Mitzvah of Zechiras Mechiyas Amalek (Chinuch, Mitzvah #603; see also Or
Same'ach, Hilchos Megilah 1:1, who explains in a similar manner).