Leviticus 13:12
And if a leprosy break out abroad in the skin, and the leprosy cover all the skin of him that hath the plague from his head even to his foot, wheresoever the priest looketh; And if a leprosy break out abroad in the skin, and the leprosy cover all the skin of him that hath the plague from his head even to his foot, wheresoever the priest looketh;
Leviticus 13:12 belongs to the laws given through Moses to ancient Israel regulating uncleanness, leprosy, cleansing, cleanliness, and sanitation for contagious or infectious diseases, including the full directions in chapter 13 and specifically verses 12-15. Leprosy was prevalent in the Holy Land, and the chapter gives especially good guidance on such diseases, addressing even germs remaining in buildings. These laws of sanitation promulgated by Moses still stand at the head of all sanitary law.
Leprosy was a horrible, dreaded, acknowledged incurable disease that could break out abroad in the skin and cover all the skin from head to foot wheresoever the priest looked. It serves as a fitting type and picture of sin as a terrible moral disease and mortal evil. Sin is transgression of the law and all unrighteousness embracing every kind of evil thing, which is rebellion against God, and which is worse than bodily leprosy.
Like leprosy spreading over the whole skin, sin is a universally prevalent, inward plague rooted within that pollutes the whole person and pervades human life. It is infectious and contagious, destructive, incurable by human means, and never gets well of itself. The sinner contaminates the very atmosphere and introduces pollution where comparative purity existed before, leading others into sin through society, an influence more to be feared than a leper's infection.
Before ritual cleansing connected with the sanctuary, a person or object had to be made visibly clean so it could be called clean. The complete cleansing of the leper from the dread malady was no less a miracle than raising the dead. It was a matter of faith in the cleansing power of the Author of the ceremonies, showing faith in Christ.
The gospel offers cleansing through Christ to those who repent and believe, and Christ's power to heal leprosy shows his power to heal. Receiving that cure requires the proud self to die, putting off the old self and putting on the new and becoming humble like a little child to receive God's kingdom. Observing sanitary law has real value for preserving life and health, and the enduring superiority of these laws proves divine guidance.
The laws of cleanliness are part of a cleansing work that corresponds to health reform as preparing clean vessels for God's Spirit and the latter rain, and Israel's example warns the remnant not to fall away from cleansing truths.