Uncleanness is not a sin in and of itself. It’s a temporary state, not a permanent state. God shows here how to go from unclean to clean, not only of ourselves but of household items, clothing, etc. God is showing us how clean He is and how we are to become like him. This isn’t about “dos and don’ts” but because He wants us to be holy and to be His people.
Deuteronomy 17 covers the type of animals to be given for sacrifice, what to do with a person who is worshiping another god and when and how they will chose a king. Deuteronomy 18 explores Levites and their inheritance, a reminder to the children of Israel that they are not allowed to “learn to imitate the detestable things of those nations” and a foretelling of a Prophet will come who is even more powerful than Moses.
The phrase “unclean” and “abomination” are different words. The reason that God introduces certain animals clean and fit to eat versus unclean and unfit to eat is a lesson to us to look at the character of the animals. The length of a woman’s purification is twice as long for a female child as a male child. Liberals claim this is about a lack of thankfulness for the female child, but the real issue is the health of the mother after childbirth.