In a contribution to Women and Water: Menstruation in Jewish Life and Law, Leslie Cook helpfully traces the differentiations of Leviticus back to the divisions of creation. 

In the creation accounts, God is differentiated from human beings and human beings from nature by “body, blood, food, time, and space” (44) and these same elements form the “building blocks” of Levitical ritual.

Cook, however, errs in the way she distinguishes violations of holiness and contracting impurity: “holiness has to do with things that for the human being are volitional, and purity has to do with things that are perceived as non-volitional” (47). Holiness is an ethical issue; though Cook doesn’t put it this way, she implies that purity is an “ontological” issue. That may be a factor in distinguishing the two, but it certainly is not the only factor. 

True, a woman who begins her period is not choosing to do so; she becomes impure involuntarily. But others in her house might become impure too, and they do so voluntarily - after all, they could leave home until her period is over. Cook strangely ignores the contagion of uncleanness, and also ignores the fact that corpse defilement and defilement by unclean food are both potentially forms of voluntary impurity.

She’s also off base, though interestingly so, in saying that impurity rules and purification rites are signals of the difference between God and human beings. She combines this with her distinction between voluntary holiness and involuntary impurity: “defines, through ethical and ritual practice, the relationship describe in Genesis between God, human beings, and nature. This definition centers around the idea that God is both holy (makes the right moral choices) and pure (does not have a body and consequently is not subject to death and organic processes). Conversely, the human being, like God, knows right from wrong and freely chooses; but the human being, unlike God, has a body that is subject to death and decay. Holiness is essentially a moral category and a representation of similarity. Impurity, generally speaking, is not a moral category but is, rather, a representation of difference” (48).

That doesn’t work because impurity is not the result of having a body per set but the result of having a body that is subject to death. The biblical term for this condition is “flesh,” and a modified version of Cook’s thesis would be that Levitical rites define the difference not between body and bodiliness but between flesh and Spirit. The rites teach Israel that “flesh and blood do not inherit the kingdom” and train them to hope for Spiritual bodies.