The Mishna (29b) taught that women are not obligated in mitzvot aseh she-hazman geramah – positive commandments that are dependent on time. 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 aseh she-hazman geramah are not obligatory for women.
The Shiṭṭah Meḳubbeẓet asks why the Gemara asks for a source freeing women from mitzvot aseh she-hazman geramah rather than asking how we know that women are obligated to perform any mitzvot aseh at all. Anyone who studies the Torah 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 Shiṭṭah Meḳubbeẓet answers that we know that the Gemara has sources indicating that women are obligated in certain mitzvot aseh she-hazman geramah (e.g. the commandment to eat matza on Pesaḥ), 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 (Shemot 19:3) ko tomar le-beit Yaakov ve-taged li-bnei Yisrael, which is understood by the Sages to mean that Moshe was obligated to teach the Torah to the women (Beit Yaakov) as well as the men (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 Beis (Beit) Yaakov based on this midrash.