Leviticus 13:11, commentary and pictures

It is an old leprosy in the skin of the flesh, an established and grave skin disease, and the priest shall pronounce him unclean and shall not shut him up or isolate him for further examination, for he is already unclean. It belongs to the laws in Leviticus 12-15 that required visible, physical uncleanness to be removed before the sanctuary could be cleansed by blood, so its law concerns the outward cleansing that prepared for the sanctuary's deeper cleansing from moral defilement. It belongs to the laws concerning leprosy and bodily cleanliness, given as sanitary instructions and laws of sanitation promulgated by Moses for dealing with leprosy. That leprosy is associated with contagious or infectious germs, and the laws required proper precautions even though God declared Himself to be the healer. Those sanitation laws still stand at the head of sanitary law, so observing them has real value in preventing disease and preserving life, and their enduring superiority proves divine inspiration guided Moses.

Leprosy is a fitting type and picture by which sin is represented, as a horrible, dreadful, terrible moral disease embracing every kind of evil thing and associated with uncleanness requiring the priest to pronounce the afflicted person unclean, where sin is the transgression of the law and all unrighteousness is sin. It also serves as a type of mortal sin. Like leprosy, sin is acknowledged as an incurable plague requiring complete cleansing, incurable by human means and never getting well of itself, infectious and contagious, destructive, and rooted within, polluting the source of life as well as bringing outward shame. Like the leper, the sinner contaminates the very atmosphere and introduces pollution where all before was comparative purity, and his society leads others to sin, so his influence is more to be feared than the infection of the leper.

Cleansing from this leprosy was considered no less a miracle than raising the dead and comes through Christ, the great Physician and Author of the ceremonies, whose blood cleanses those who repent and believe when received by faith in His cleansing power, so the rites show faith in Christ. Healing requires the proud self to die and the old person to be put off and the new put on. Christ's healing of lepers shows His power to heal.