What does leprosy show about what sin does?
Leprosy serves as a picture of sin, illustrating that sin is a filthy thing that defiles. The horrible, final stages of leprosy, beyond comprehension, show what sin does—it corrupts and destroys. Throughout the Law of Moses, constant washing taught Israel that sin was reckoned as filthy.
Les explains that in the Old Testament economy, priests had to wash repeatedly before entering service or the Day of Atonement. That constant washing showed Israel that sin was a filthy thing. He teaches that leprosy is used as a picture of sin because of how horrible a leprous person can look, especially in the final stages. It was beyond comprehension, and that is what sin does. He also recalls Naaman the Syrian general, who had leprosy and was told by the prophet to dip in Jordan seven times. Though Naaman objected, he obeyed and was healed of his leprosy.