Moussar sur Les Nombres 5:2

וישלחו מן המחנה . What is meant is that והיה מחניך קדוש, the impure, should be sent from all three camps, as the situation required, in order to comply with the Torah's instructions in Deut. 23,15, והיה מחניך קדוש, "your camp shall remain holy." The Zohar there explains that the reference is to the 248 limbs of a person which make up his skeleton and which must retain their sanctity. This is hinted at in our paragraph. There are three camps and they represent respectively the head, the heart, and the stomach. The head is the seat of the brain and of all thoughts, and this domain must not be polluted by even the most minor degree of impurity. Our sages have already taught us that the הרהורי עבירה, impure thoughts and intentions, are more dangerous morally than the actual impurity caused by committing the sin (Yuma 29a). There follows the camp of the Levites, which is comparable to the heart of man. Obviously a good and pure heart is to be maintained at all times. The third camp is comparable to man's stomach and intestines, an area vital for converting food into energy, and discharge of that which cannot be used constructively. This area is somewhat ugly; it reminds us constantly of the bodily aspects of man and our tragic inability to remain alive without the body. Nonetheless, anyone who suffers from severe types of impurity must leave even that part of the camp. The moral lesson of all this is to sanctify oneself by means of one's food intake or abstention from it. The Jew is commanded to observe modesty even when he performs biological functions that are necessary, such as excretions of undigested food. All of these rules are designed to expel serious impurities.

Parshat Nasso, commences with commandment 362, that people who have become defiled are required to leave the camp, as it says (5,1) וישלחו מן המחנה people who suffer from serious impurities such as טומאת זב, טומאת מת, or צרעת.