The Greek word translated as "will" means "to consent" and "to be resolved to a purpose". The English phrase "I will" is easy to confuse with an indication of doing something in the future because that is how "will" is commonly used in English. But in Greek, Christ is not saying that he is going to be doing something in the future. The Greek word does not work the same as the helper verb "will" in English. Its primary purpose is to express consent and even a delight in doing something. It doesn't even mean "desiring" or "wanting" to do something. It means "I consent" or "I resolve to do so."
The Greek verb translated as "be clean," means to remove dirt. It is a passive command. Using "cleansed" makes its role as a verb clearer. It is used for a lot of specific types of "cleaning" including cleansing a person of leprosy but it also has a general meaning of "purifying" anything. It is in the form of a command. Both the leper and readers today are told to become pure of contaminants.