We are commanded regarding the laws of the Mei Nidah [the waters in which the ashes of the Red Heifer have been mixed]; the conditions under which they purify [one who is ritually impure as a result of contact with a corpse] and the conditions under which they cause ritual impurity [to the one who handles them].
The mitzvah regarding the ritual impurity of the metzora (a person suffering from tzaraat, a skin discoloration described in the Torah). This mitzvah includes all the laws applicable to this impurity: what types [of discolorations render a person] impure, and [what types do not]; which types of this impurity require quarantine, and which do not; the laws associated with the quarantine, i.e., shaving [the hair surrounding a tzaraat lesion in an area of hair]; and all other laws associate with tzaraat and the gradations of its impurity.
