Lepers were considered "dead men walking", and were banished from towns and villages. For a leper to approach someone without the disease was to bring about a death sentence upon himself (someone who couldn't be trusted with staying away from infecting people had to be killed for the good of society). The opening prayer for the First Week of Ordinary Time asks God to help us to do His will with "courage and faith". For this leper to approach Jesus took both of those things; he was either going to get cured or get killed.
Put yourself in the sandals of Peter, Andrew, James, and John, when the leper approaches Jesus. There would be no surprise; they probably would have smelled the leper before they saw him. The face, hands and feet become a mass of nodules. The muscles and tendons contract until the hands look more like claws. The vocal chords ulcerate and so the voice becomes hoarse and breathing is more like wheezing. The muscles around the eyes deteriorate so that the leper can only stare straight forward. Discolored patches would appear on the skin, that eventually putrify.
THAT'S what approaches Jesus.
Mark (but really Peter) tells us the man knelt before Jesus, which could not have been easy to do with his muscles. He speaks to Jesus, forcing words through those vocal chords. But more than that, we read that Jesus stretches out his hand and touches him! He didn't have to touch the possessed man a few verses before in order to heal him. He didn't have to tough the leper; he wanted to. Maybe to give this man the first human contact he's probably had in years. Maybe to freak out the Apostles. Maybe both.
For whatever reason(s) he did it, what Mark tells us next must have been amazing to watch: "The leprosy left him immediately". Imagine seeing what the Apostles saw: leather-like skin turning pink, muscles growing, wheezing stopping, his voice clear. It had to have made them all speechless.
What ailment do you have? What eats at your body (or soul)? Have you knelt in front of the Lord and begged him, saying, "If you wish, you can make me clean"?
Now the extra credit: What if he doesn't wish to heal you? What if he says to you, like St. Paul, "My grace is sufficient for you to heal yourself"? Would you still love him? What is, rather than saying "no", the Lord is saying "not yet"? Do you have the patience?