| Gill's Exposition of the Entire Bible To teach when it is unclean, and when it is clean,.... A man, his garment, or his house; for it respects them all, as Aben Ezra observes; which was the business of the priests to teach men, and they by the above laws and rules were instructed how to judge of cases, and by which they were capable of pronouncing persons or things clean or unclean: this is the law of leprosy; respecting every sort of it, and which is very remarkably enlarged upon.
Geneva Study BibleTo teach when it is unclean, and when it is clean: this is the law of leprosy.
Wesley's Notes 14:57 To teach - To direct the priest when to pronounce a person or house clean or unclean. So it was not left to the priests power or will, but they were tied to plain rules, such as the people might discern no less than the priest.
King James Translators' Noteswhen it is unclean...: Heb. in the day of the unclean, and in the day of the clean
Matthew Henry's Concise Commentary14:54-57 When that God who is rich in mercy, for his great love wherewith he loved us, even when we were dead in sins, hath quickened us by his grace, Eph 2:4,5, we shall manifest the change by repenting, and forsaking former sins. Let us follow after holiness, and let us compassionate other poor lepers, and desire, seek, and pray for their cleansing. | 
