The Torah in Parashat Mesora (Vayikra 15:26-29) discusses the process of purification that a woman must undergo after becoming a “Zaba Gedola.” The status of Zaba Gedola is attained when a woman experiences bleeding for three consecutive days during the time of month when menstruation is not expected, such that this bleeding signifies some form of illness. After seven days without experiencing any bleeding, the woman brings a sacrifice – specifically, two birds – and is then considered Tehora (pure). The Sefer Ha’hinuch lists this sacrifice as the 183rd Biblical command.
The Torah requires also a “Zab” – a man who experiences an unusual bodily discharge – to bring this same sacrifice as part of his purification process. Interestingly, the Rambam lists these two sacrifices – that of the Zab, and that of the Zaba Gedola – as two separate Misvot, even though they are identical, and they are brought for the same reason. The Sefer Ha’hinuch explains that these are counted as separate Misvot because these two statuses of Tum’a (impurity) are very different from one another. A woman becomes a Zaba as a result of a flow of blood, whereas a man becomes a Zab as a result of an unusual white discharge. Since these two phenomena differ significantly from one another, the Rambam lists the sacrifices required of a Zab and a Zaba as distinct Misvot. This is in contrast to the sacrifice required by a Mesora as part of his or her purification process. A man and woman, quite obviously, experience Sara’at identically, and thus a male Mesora’s sacrifice and a female Mesora’s sacrifice are considered a single Misva. But the statuses of Zab and Zaba result from two entirely different biological phenomena, and the Rambam therefore lists these sacrifices as separate Misvot.
This Misva applies only in the times of the Bet Ha’mikdash. A woman who became a Zaba Gedola and failed to offer the purification sacrifice has violated this affirmative command. She also retains her status of Tum’a, and it thus remains forbidden for her to partake of hallowed food and to enter the site of the Bet Ha’mikdash.