18 "If the body develops a boil in the skin, and it is healed, 19 and in the place of the boil there comes a white swelling or a bright spot, reddish-white, then it shall be shown to the priest; 20 and if, when the priest sees it, it indeed appears deeper than the skin, and its hair has turned white, the priest shall pronounce him unclean. It is a leprous sore which has broken out of the boil. 21 But if the priest examines it, and indeed there are no white hairs in it, and it is not deeper than the skin, but has faded, then the priest shall isolate him seven days; 22 and if it should at all spread over the skin, then the priest shall pronounce him unclean. It is a leprous sore. 23 But if the bright spot stays in one place, and has not spread, it is the scar of the boil; and the priest shall pronounce him 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.