Cleansing: skin diseases, molds and discharges. Rules and procedures. The takeaway for me is being “unclean” marks you as an outcast, an untouchable. This might last until evening, a week or more depending on what unclean event has occurred. While there were probably practical reasons for all of these rules, it seems important to appreciate how the Jewish mindset is established with this heritage. By the time Jesus appears on the scene, people have spent hundreds of years incorporating various laws that identified those seen as clean and unclean. (It’s interesting that the opposite of clean is not dirty, yes?)
For 430 years the people that Moses was leading were slaves in Egypt, they had learned Egyptian ways, slaves born of slaves. God allowed this to continue for a very long time (in earthly terms), now he is reshaping his people. I don’t understand the remediation of the unclean events, but I can appreciate the need for order and discipline.