In a deep irony the essence of the covenantal relationship is purification. The waste of one covenantal partner is purified by the consumption of the other covenantal partner so that the one partner can partake of the product while the other partner partakes of the waste. Indeed, the very definition of otherness might well be that one species' waste is the other species' oxygen.
Purification is the process by which what is toxic is transformed into that which is life sustaining. The instrument of that transformation is the covenantal partner. The process of purification has within it the expression of this contradiction – that what is toxic to one is life-giving to the other. Hence the contradiction of the Red Heifer, where what purifies is itself contaminated.