Q: Please throw light on the question: after giving birth to a boy, mother is not permitted to enter Sanctuary for 40 days, this prohibition extends to 80 days in the case of a girl. Why the difference? Is there a reason that will not offend our feminist sisters?
A: Although there is a certain spiritual impurity after childbirth that extends for a double period after the birth of a girl, at the very same time there is a complementary law in the Torah that for the entire 80 day period for a girl, the blood which the woman sees is pure blood. Thus she is permitted to have relationships with her husband during this entire time. That zivug lasts for a double period as opposed to after the birth of a boy, when her blood is pure, i.e. she can maintain relations with her husband only for 40 days. After the initial 7 days when she goes to the mikvah she is pure for 40 days after the birth of a boy, and after the birth of a girl for 80 days.
The deep reason is that a female represents kelim, vessels. A boy represents lights. The origin of vessels is higher and double with respect to the origin of the lights. That is why there are many things about a female that are double with respect to a male. This double is positive. It is like a ba'al teshuva who is kiflayim l'tushia, twice as good. Even though there is this one implication of not coming to the sanctuary for a double period of time, the opposite double, that the woman is pure for a double period of time is because of the doubly high origin of vessels as opposed to the lights that fill the vessels.