Tefillin - Women
Why have women not traditionally worn tefillin? Can I do so if I desire?
The Aish Rabbi Replies
It is a general principle that women are exempt from certain mitzvahs (specifically, time-bound positive commands). An example of this is the mitzvah of tefillin, which men are required to wear.
The Torah forbids women to wear garments that are made specifically for a man, as it is written, "A man's garment shall not be worn by a woman." (Deut. 22:5) The Talmudic Sage, Yonatan Ben Uziel, in his Aramaic translation and explanation of the Torah, states that this verse refers to tefillin and tzitzit. Therefore if a woman wore tefillin and tzitzit which are men's garments, she would be breaking a Torah law.
Rabbi Aryeh Kaplan explains women already have the mitzvah of tefillin incorporated into their spiritual makeup, and thus don't need to wear it.
The reason for the commandments is to establish a link with God. The most profound way to do this is to resemble Him. There is one unique way that women resemble God in a way that no man could ever hope to. Only a woman can create within her body. Only a woman can bear a child. In this sense, a woman partakes of God's attributes more intimately than any man.
The Kabbalists teach that the hand tefillin represents the feminine element. The single box (that contains the parchment) can be said to represent the womb, and the leather straps wrapped around the arm, the umbilical cord. What men partakes of with an object, women partake of with her body.
There are two basic elements in Judaism, the home and the synagogue. Unlike other religions where the church is primary, Judaism treats the home and synagogue as being co-equal. Some of our most important rituals belong exclusively to the home, such as the Seder, the Sukkah, the Shabbat table, and the Chanukah menorah. The continuity of Judaism rests on the home more than anything else. The Hebrew word for home is "bayit."
The box of Tefillin is called a bayit - literally a house. The woman also has her bayit - the home in which she raises a family.
Further, the Mishnah Berurah 38:3 explains that tefillin should not be worn on a voluntary basis because they must be worn while maintaining a pure mind and pure body. For this reason, one may not forget that they are on him and may not sleep or pass wind while wearing them. (In fact, if men were not obligated to wear tefillin, they also would not risk doing so!)
I hope this helps explain.