Question: Can you direct me to a treatise on the evolution of the practice of ritual purification (childbirth, skin diseases, and secretions) following the destruction of the Second Temple?

Answer: Hi! The Talmud Shabbat says that the laws of ritual purification have “that on which to rely”, as opposed to the laws of the Sabbath, for example, which are “mountains hung by a hair”. Meaning, some things have much more explicit sources in the written Torah, and others were mostly taught through the oral Torah. Ritual purification (“tum’ah” and “taharah”), then, is one of the ones where there is a wealth of information in the written Torah. As such, its observance goes back to antiquity, and we have numerous verses in the bible touching on it.

However, after the destruction of the second Temple, much of the impetus for observing those laws was lost, since the main impacts of being tahor were (a) the ability to go into the Temple and (b) to eat sacrifices. Further, the very ability to become pure became more and more limited, as anyone who came into contact with the dead, even being in the same building as a dead person, became tamei in a way unfixable except with the ashes of the red heifer. Since that could not be brought in the absence of the Temple, it eventually became impossible to observe most of these laws, until the Temple is rebuilt.

The sages of the Mishnah and the Gemara nonetheless faithfully recorded their traditions on how to keep these laws, even though they were not able to do it themselves (they did the same for the laws of bringing sacrifices.) Two good places to see their descriptions are Tractate Chagigah and all the Mishnayos in the Seder of Taharos.

Best wishes,
Michoel Reach