Various skin diseases are examined by the priest, who declares them either safe, under quarantine for a week usually for further inspection then, or unclean and to live apart until healed.
If you are healed you kill one bird ritually and release another. You wash, shave your head hair, wait 7 days, then shave it all off. Then you sacrifice 3 lambs with a grain offering (1, if you can't afford 3).
If a house has mold or mildew, you do the same thing. The priest comes and inspects and declares it either clean, under quarantine for a week, or unclean and to be destroyed.
How this is about Jesus
Jesus follows this general principle in His visitation of Israel and Jerusalem. His teaching declares their life and doctrine unclean early on. He comes to Jerusalem and declares them unclean again. He returns in 70 AD and destroys the house. It is thoroughly diseased.
Sins this reveals
We often minimize our sin, saying it's only skin deep, when it really goes to the heart. We are cherishing and reveling in some sin, instead of coming across it incidentally or mortifying it.