John Calvin Commentary Deuteronomy 23:10

"If there be among you any man, that is not clean by reason of that which chanceth him by night, then shall he go abroad out of the camp, he shall not come within the camp:" — Deuteronomy 23:10 (ASV)

If there be among you. He enumerates two kinds of pollution, by which the Israelites may know what is meant by their keeping from the “wicked thing.” First, He pronounces unclean, and casts out of the camp those who may have had a filthy dream, until they have washed themselves in the evening. Secondly, He forbids them to defile the camp with what passes from the bowels; and not only this, but even when they have gone outside the camp, He commands them to bury their excrement beneath the earth, lest any filthiness appear.

Yet it is probable that, by synecdoche, everything is referred to which made men unclean and polluted. But Moses, speaking to soldiers, considered it sufficient to tell them briefly that, although they might be occupied with war, cleanliness must still be attended to. By “what chanceth at night,” all are agreed in understanding a flow of semen; from which we infer how greatly impurity defiles a man, since uncleanness is contracted even from foul dreams.

Regarding the second part, some desire to appear quick and clever by attacking Moses because he has introduced among the precepts of holiness that no one should relieve his bowels in the camp. Indeed, they say, the smell might offend the nostrils of God! But their silly impudence is easily refuted, for God would by such basic rules keep His ancient people in the way of duty, lest liberty even in the most trifling things should lead them onward to audacity. If they had been permitted to defile every part of the camp, the people would soon have been hardened to filthiness of every kind. Thus they were held back by this rein, so that they might more earnestly apply their minds to spiritual integrity.

Those also are mistaken who suppose that this was a sanitary precaution, so that the smell would not produce diseases and be injurious to their bodily health. For Moses plainly declares that he not only considered what was wholesome, or even what was decent in the eyes of men, but rather that he would accustom the people to abhor uncleanness and to keep themselves pure and unpolluted—for he adds that God presided in the camp to protect them from the power and assaults of their enemies, and that they should fear that if they contaminated the camp, He would be offended by their filthiness and forsake them.

In summary, when they need God’s assistance and are engaged in war against their enemies, the pursuit of holiness must not be omitted or neglected even in the midst of arms.