Metzora: Why Does The Torah discuss such things?

In this Torah portion, the priests are instructed in how to ritually cleanse one stricken with tsara'at, often mistranslated as leprosy, but when it affects people is closer to plaque psoriasis, and when it affects clothing or houses is closer to mildew or dry rot. There is instruction in how to recognize if a house is afflicted with tsara'at, and when it should be demolished to ward off the affliction. The rest of the Torah portion discusses male and female genital discharges, and how they make a person ritually impure.

For men, genital discharges, both from semen and from gonorrhea, are discussed. For women, menses, and non-menstrual bloody discharges are discussed. It is enough to have a nocturnal emission or a discharge of pre-seminal fluid to render a man in a ritually unready state, but sexual intercourse leading to a male ejaculation, or a discharge resulting from gonorrhea will also cause a man to lose his spiritual readiness. In the case of gonorrhea, he will remain unready for a week after the last discharge. Also, if a man has intercourse with a menstruating woman, he is regarded as being in the same state of ritual unreadiness as a menstruating women for a week after the intercourse. In each case, ritual bathing and sacrifices are necessary to put them back in a state of spiritual and ritual readiness.

For women, their menses renders them in a ritually unready state for a week after the last discharge. They are also rendered unready by any bloody discharge, even if outside of her menstrual cycle. After bathing and bringing turtle doves to the priests to sacrifice, they are ready again.

This stuff is crazy at first glance. What is going on here? Why is this in the Bible?

The common factor is the intermediation of the priests. When something strange and probably unhygienic happens, bring in someone who is experienced in dealing with such things (read "doctor" here), and let them examine it. Then bathe and disinfect. Not bad advice. This was a superstitious age. To bring in an objective party and to stress bathing, quarantine for contagious afflictions, and a clear, delineated way to get back to normal is a big improvement for a people used to moral panics, child sacrifices, and mad eruptions of violence.

The Torah portion ends with the reason for all the purity laws. The Tabernacle is pure, and the people who come into the Tabernacle are unleashing powerful spiritual energies, powerful enough to kill the unready. Those who come into the Tabernacle should be in a state of spiritual readiness. When you enter the tyled lodge, you should be in a similar state of spiritual readiness.