18 "If anyone has a boil on the skin that has started to heal, 19 but a white swelling or a reddish white spot develops in its place, that person must go to the priest to be examined. 20 If the priest examines it and finds it to be more than skin-deep, and if the hair in the affected area has turned white, the priest must pronounce the person ceremonially unclean. The boil has become a serious skin disease. 21 But if the priest finds no white hair on the affected area and the problem appears to be no more than skin-deep and has faded, the priest must quarantine the person for seven days. 22 If during that time the affected area spreads on the skin, the priest must pronounce the person ceremonially unclean, because it is a serious disease. 23 But if the area grows no larger and does not spread, it is merely the scar from the boil, and the priest will pronounce the person ceremonially clean.
Matthew Henry's Commentary on Leviticus 13:18-23
Commentary on Leviticus 13:18-44
(Read Leviticus 13:18-44)
The priest is told what judgment to make, if there were any appearance of a leprosy in old sores; and such is the danger of those who having escaped the pollutions of the world are again entangled therein. Or, in a burn by accident, verse 24. The burning of strife and contention often occasions the rising and breaking out of that corruption, which proves that men are unclean. Human life lies exposed to many grievances. With what troops of diseases are we beset on every side; and thy all entered by sin! If the constitution be healthy, and the body lively and easy, we are bound to glorify God with our bodies. Particular note was taken of the leprosy, if in the head. If the leprosy of sin has seized the head; if the judgment be corrupted, and wicked principles, which support wicked practices, are embraced, it is utter uncleanness, from which few are cleansed. Soundness in the faith keeps leprosy from the head.