In the Old Testament, being ceremonially clean was part of being holy. Being clean in the eyes of the law was a fragile thing, because touching anything unclean made the one who touched it unclean. That’s why a leper in Israel had to live away from everyone else--so nobody would touch him and become unclean. We’re not talking about actually catching leprosy. Touching a leper made you unclean, even if you didn’t catch the disease. In other words, uncleanliness itself was contagious.
And then Jesus came along and changed everything. When Jesus touched a man with leprosy, the leper was healed and Jesus didn’t become unclean. It seems that when Jesus is involved, it’s cleanliness that’s contagious.
(c) Copyright 2007, A. Milton Stanley