Chapter 13 of Leviticus deals with contagious skin diseases. The instructions for the priest are to inspect infected areas and watch specifically for it to spread. Leprosy always spread. I expect that cancer today is the modern equivalence to biblical leprosy. The New Testament compares Leprosy with sin. From this chapter we can learn two important things about sin.
First, sin is deeper than the skin. It goes all the way to the heart. I’ve been quoting Jeremiah 17:9, “the heart is deceitful above all things and desperately wicked. Who can know it?” It’s interesting to notice that the Hebrew word we translate as “wicked” in that verse is the word that is also translated “sick.” The NIV actually translates it “without cure.” Wiersbe says, “Those who talk about the innate goodness of man know neither the Bible nor their own hearts.

Second, sin is contagious. It spreads. Contagious diseases are always quarantined today because if you are exposed, the chances are good you will come down with it. Like the rot in an apple, it always spreads to the good apples and infects them. Thus Paul exhorts his readers, “do not be deceived, bad company corrupts good morals.” (1 Corinthians 15:33)
But that’s not the case with Jesus. It’s not that he’s “clean” in the way a person might be declared clean. That would simply mean the absence of some disease. No, Jesus was the actual source of all cleanliness. It’s not that “bad” was lacking. It’s that all good, health and wholesomeness were present. When he touched the diseased, he reversed the process. His “healthiness” became contagious. He passed on his wholeness to the sick, lamb, blind, and deformed. It’s interesting to notice that Jesus often added “your sin is forgiven” when he performed physical healing.  Jesus’ healing went beyond the skin, it penetrates the heart. The “sickness” of man’s heart now becomes curable!
“Have you been to Jesus for the healing power? Are you washed in the blood of the Lamb?”