And a leper came to him, imploring him, and kneeling said to him, “If you will, you can make me clean.” Moved with pity, he stretched out his hand and touched him and said to him, “I will; be clean.” And immediately the leprosy left him, and he was made clean. And Jesus sternly charged him and sent him away at once, and said to him, “See that you say nothing to anyone, but go, show yourself to the priest and offer for your cleansing what Moses commanded, for a proof to them.”
(Mark 1:40-44 ESV)
Leprosy is not a common disease back then, and not just a normal illness. Having leprosy in the community of Israel means expulsion form Israelites community. They will be put outside the community, and are not allowed to be touched for fearing that the illness will infect other people. No one will want to touch them, and they will have to warn people whenever they’re around by crying “unclean, unclean.”
He is a leprous man, he is unclean. The priest must pronounce him unclean; his disease is on his head.
The leprous person who has the disease shall wear torn clothes and let the hair of his head hang loose, and he shall cover his upper lip and cry out, ‘Unclean, unclean.’ He shall remain unclean as long as he has the disease. He is unclean. He shall live alone. His dwelling shall be outside the camp.
(Leviticus 13:44-46 ESV)
So Jesus’ act of healing the man with leprosy is not just a mere healing, but also shows his mercy and willingness to accept someone who is sick and rejected!
Jesus also told him to report back to the priest, just like what Moses commanded in the book of Leviticus chapter 14.