איש איש כי יהיה זב מבשרו, “any man who will have a discharge from his flesh, etc.” Nachmanides writes that the reason why a discharge from the male genitals is ritually impure and he needs to bring an offering when he has recovered, is that it is one of the most infectious diseases and he needs to bring a thanksgiving offering for having recovered from this disease at all. The sin offering, by means of which he acknowledges that had he not been guilty of a sin he would not have been afflicted with this disease, is meant to assure him that he will not become the victim of further diseases. The reason that male sperm is altogether something that is ritually impure and confers ritual impurity on contact etc., although it is a basic and natural activity, is rooted in the very nature of the act of sexual intercourse as the means by which man assure himself of progeny. It is analogous to the ritual impurity caused by and conferred by the dead. The very essence of a human being’s body is the source of its corruption. He who does lie with a woman and impregnates her, has no way of knowing whether he has destroyed his sperm in the process, or whether it will take root in the partner’s ovum and produce a new life. The Torah imposed a lesser degree of ritual impurity on a woman that has been afflicted with a similar discharge from her womb at regular intervals when she menstruates, proof that her most recent opportunity to be inseminated had failed to achieve its purpose, seeing that with her such symptoms are part of her natural life cycle, at any rate. She does not have to bring a sacrifice expressing her gratitude for having been healed, as the phenomena she experienced were not in the nature of a disease. The Torah therefore imposes on her a period of ritual impurity for seven days, regardless of her flow of blood (or discharge) having ceased earlier than that. Normally, such a flow of menstrual blood does not continue for more than seven days. However, if her discharge continues beyond the seven days that she normally discharges menstrual blood, she is clearly experiencing a disease, and upon being cured has to offer a sacrifice acknowledging that G’d had healed her, similar to the male zav having to bring such a sacrifice. In the case of the female suffering the disease described as zav or zavah, the Torah does not spell out the need for ritual immersion by the afflicted woman, as the comparisons drawn by the Torah between the male suffering this disease and the female suffering it make it plain that their processes of purification are similar, except that the male must bathe in spring water whereas the woman need only immerse herself in a ritual bath, a mikveh, water in contact with rainwater or other water that has not had a chance to become ritually contaminated. According to the plain meaning of the text the woman would have to bathe herself in spring water just as the male suffering from that disease, however our sages ruled that she need not bathe in spring water. They derived the reason for their ruling from the extraneous words ואחר תטהר, “and afterwards she becomes ritually pure” (verse 28) There was really no need to add these words as a woman is included in the legislation and the verse only wanted to make a distinction in the mechanics of her purification rites and those of the male. The discharge of a woman called זבה, consist of blood, whereas the discharge of her male counterpart consist of a whitish fluid similar to the colour of semen. In the case of a woman the time of the month when such unexpected discharge occurs is of the essence in determining whether this discharge is part of her menstrual cycle. The word ואחר means that although her purification rites did not involve spring water nonetheless she becomes purified by immersing herself in the same kind of water that purifies her at the end of her monthly menstruation.תטהר.

וידיו לא שטף במים, “without having rinsed his hands in water.” Nachmanides writes that in this instance the Torah uses the word שטף to describe immersion in the purifying waters of the mikveh. The same expression had been used by the Torah for someone instead of immersing his body, immersing his ritually contaminated vessels.