The Book of Leviticus.

You cannot make the unclean person or thing holy, but an unclean person or thing can make the holy unclean.

The title is better translated, About or Concerning the Levites.
The book covers roughly a month of the journey after leaving Egypt. It’s an exciting narrative that points you to Jesus as you learn the connection between the Law and Grace, and how it applies to Christians in the modern age.