In cases of infectious skin diseases, be careful to diligently follow everything the Levitical priests instruct you. Be careful to do as I have commanded them.
KJV
Take heed in the plague of leprosy, that thou observe diligently, and do according to all that the priests the Levites shall teach you: as I commanded them, [so] ye shall observe to do.
ASV
Take heed in the plague of leprosy, that thou observe diligently, and do according to all that the priests the Levites shall teach you: as I commanded them, so ye shall observe to do.