At first reading the doctrine of uncleanness taught in the book of Numbers is similar to notions of physical and moral impurity in other religions. Considered more closely in a comparative framework, the biblical idea of impurity is unusual. To make a coherent anthropological interpretation a new reading has to be developed. The book of Numbers is composed according to an archaic literary form. Twelve alternating sections of law and narrative run in parallel across the whole book. The many repetitions and confusions which have been attributed to editorial carelessness now appear to be rhetorical devices to mark structural shifts and make the macro-compositional pattern. Read through this literary structure the message of the book is transformed. The priestly editors cannot be interpreted as an elitist group mainly concerned with the preservation of their cultic privileges. Their message is the joyful one that all the prophecies have been fulfilled and that all the sons of Jacob shall be heirs to the promise. Purity rules are generally used to justify social ranking and discrimination, but Numbers gives no scope for such a usage. The book announces a liberal theology with a benign doctrine of purification available for all who wanted it.