Matthew 8:2

If thou wilt (ean qelh). The leper knew that Jesus had the power to heal him. His doubt was about his willingness. "Men more easily believe in miraculous power than in miraculous love" (Bruce). This is a condition of the third class (undetermined, but with prospect of being determined), a hopeful doubt at any rate. Jesus accepted his challenge by "I will." The command to "tell no one" was to suppress excitement and prevent hostility.