Lawrence H. Schiffman, From Text to Tradition, Ktav Publishing House, Hoboken, NJ, 1991.

In biblical and Second Temple times the entire system of ritual purity and impurity, as outlined in the levitical codes of the Torah, was in effect. The system of ritual purity and impurity is based on the notion that certain bodily discharges, physical experiences, diseases, and animals can render one impure. Being impure means that one cannot approach the sancta, the Temple, and, in the case of menstruation, that one must abstain from sexual relations. The various purification rituals—quarantine, sprinkling, shaving, laundering of clothes, immersion in a ritual bath—can return the impure person to a state of ritual purity, and thus to full participation in family life and Temple worship.

By applying themselves to detailed study of the purity laws even after the destruction of the Temple, the tannaim indicated that in their view the observance of these laws would once again be the norm in the perfect society of the messianic future. Nonetheless, the destruction was followed by a gradual period of transition in which it became clear that virtually all of these laws had become inapplicable. Despite this, ritual purity remained in force in two major domains, the washing of the hands before eating bread (a rabbinic ordinance) and the observance of menstrual purification in marriage.

The Torah had required that a seven-day purification period, followed by immersion in a mikveh (ritual bath), take place after the onset of menstruation. Around the end of the tannaitic period or the beginning of the amoraic, because of the possibility of confusing menstruation with a flow of non-menstrual blood (which required a seven-day waiting period before immersion), it was decided that the counting of the seven days was to begin after the menstrual flow had ended.

This resulted in the system of ritual purification still followed in Judaism. It works as follows. From the onset of her menstrual period, the woman is impure for at least five days. Thereafter, when the flow stops, she begins to count seven days in which there is no flow. When those days are completed, on the night after the seventh day, she immerses and returns to having sexual relations with her husband. Although these laws are to be observed by the woman, the man violates a prohibition of the Torah if he has relations with his wife when she is ritually impure.

In Second Temple times, certain groups, such as the author or authors of the Temple Scroll from Qumran, sought to completely separate menstruating women from the community. Further, certain rabbinic works reflect a tendency to regard the menstrually impure woman as a source of impurity and even as an object of disgust. These approaches were clearly on the decline in the amoraic period and were preserved thereafter only in sectarian circles, including those which came together to form the Karaite movement in the early Middle Ages.

Women, then, became the guardians of the remnants of the vast system of purity which had existed in the days of the Temple. In amoraic times, as is clear from aggadic material, menstrual purity came to symbolize the notion that family and home life had to aspire to the purity of the Temple. Indeed, the home itself, and specifically the marriage relationship, became another sanctuary which the Jews could carry with them and which would help to sustain them in the millennia ahead.