The Mishnah (Kiddushin 29b) taught that women are not obligated to perform positive commandments that are dependent on time (“mitzvot aseh she-hazman geramah”).
Our Gemara asks for a source that frees women from these commandments, and presents tefillin as the archetype:
Just as women are not obligated to lay tefillin, similarly all mitzvot “positive commandments that are dependent on time” are not obligatory for women.
The Shittah Mekubetzet (Rabbi Betzalel of Tzfat, c.1520-1591) questions why the Gemara asks for a source freeing women from “positive commandments that are dependent on time” rather than asking how we know that women are obligated to perform any positive mitzvot at all.
Anyone who studies theTorah knows that it is written in the masculine, and appears to be directing its commands to men.
Furthermore, the Gemara later on (35b) feels obligated to prove that women are obligated to refrain from negative commandments (mitzvot lo ta’aseh).
The Shittah Mekubetzet answers that we know that the Gemara has sources indicating that women are obligated in certain positive commandments that are dependent on time (e.g. the commandment to eat matzah on Pesach), thus it is only natural that the Gemara would seek a source for the fact that women are not obligated in other mitzvot.
He also points out that the entire question is predicated on a misunderstanding of the foundation of the Torah, since it is well known that the Torah was given to the entire Jewish People – men and women – based on the passage (Exodus 19:3) “This is what you must say to the family of Jacob and tell the Israelites”, which is understood by the Sages to mean that Moshe was obligated to teach the Torah to the women (referred to as Bet Yaakov) as well as the men (referred to as Bnei Yisrael).
It is interesting to note that the 20th century movement of formal Torah schooling for women that was the brainchild of Sarah Schenirer, who recognized that in the modern age in order to ensure that women kept mitzvot it was essential that girls join their brothers in the study of Torah, was called Bet Yakov based on this midrash.
–Rabbi Adin Steinsaltz