In his first book, Impurity and Sin in Ancient Judaism, Jonathan Klawans explores the complex relations of sin and impurity in biblical law and later Jewish thought. 

He distinguishes between “ritual defilement” that arises from unavoidable natural processes and “moral defilement” that arises from sin. In Purity, Sacrifice, and the Temple, he summarizes some of his findings as follows: “Ritual defilement concerns those things that threaten the status vis-a-vis the sanctuary of the individuals directly affected. Those who are ritually defiled, those whom they ritually defile, and those animals that, when dead, are considered ritually defiling - all of these are banned from the sanctuary” (71).

Moral defilement, however threatens “not only the status of the individuals in question but also the land and in turn the sanctuary itself.” Moral impurities are abominations that might provoke Yahweh to leave His house and cause the land to spew Israel into exile (71).

For Christian theology, this distinction raises some important questions: Does the distinction of ritual and moral impurity continue into the New Testament and the church? What might ritual purity entail in a world after the cross? And if the distinction doesn’t pertain, if it collapses into one complex category or if the Hebraic dualism of ritual and moral defilement is reduced to the single category of moral defilement, what does that imply about the impact of our sin? Do all forms of impurity threaten the church in the same way that moral impurity threatened Israel?