When the host goeth forth. What he had taught with respect to the preservation of purity at home, and in time of peace, he now extends to times of war also, so that they might keep themselves clean from all defilement even in the midst of the clang of arms. We know how greatly laws are disregarded during war, when all things are under the control of violence rather than reason; and we know that much license is wont to be given to soldiers, which would be by no means tolerated in peace. God would remedy this evil by requiring the Israelites to aim at the same purity in war as in peace; for this is a special law which forbids their being dissolute and unruly in war-time, as He has before condemned all impurity in general, as if He had said, that under no pretext would they be excusable, if they neglect the duty of cultivating habits of purity. For He does not command them to be cautious in the army and in the camp, as if they might sin with impunity when at home, but admonishes them that God would by no means excuse them although they should allege the necessity of war. Much more would the crime be aggravated, if they should pollute themselves in peace and when their minds were calm. Whence we gather that it is vain to catch at empty excuses for the violation of God's commands in any respect; for, however difficult the performance of duty may be, still God never resigns His rights. Now, if war, which seems to dispense with laws, does not excuse crime, much greater, as I have said, shall their guilt be accounted, who in a tranquil condition of life are licentiously carried away by sin.

The whole passage refers not to the encampments of the nation while passing from Egypt through the wilderness, but to future warlike expeditions seat out from Canaan.

When the host goeth forth against thine enemies,.... An army of soldiers march in order to meet the enemy and fight him:
then keep thee from every wicked thing; the Targum of Jonathan adds, by way of explanation,"from strange worship, uncovering of nakedness, and from shedding innocent blood;''that is, from idolatry, uncleanness of every sort, and murder; and all other wickednesses ought to be abstained from at all times by all persons, but especially by soldiers in such a circumstance, just going to battle; since sin committed weakens natural courage, as it loads the conscience with guilt; and since victory and success, which depend upon the blessing of God on arms, cannot be reasonably expected, where vices of all sorts are indulged and abound; and especially seeing such are about to expose their lives to the utmost danger, and know not but that in a few hours they must exchange this life for another, and appear before God, the Judge of all, against whom they sin; and yet how little are these things thought of by such in common! it was the wisdom of the Jewish legislature, which was of God, to inculcate such things into the minds of their soldiers.

The camp of the Lord must have nothing offensive in it. If there must be this care taken to preserve the body clean, much more should we be careful to keep the mind pure.

When the host goeth forth against thine enemies, then keep thee from every wicked thing--from the excesses incident to camp life, as well as from habits of personal neglect and impurity.

Preservation of the Purity of the Camp in Time of War. - The bodily appearance of the people was also to correspond to the sacredness of Israel as the congregation of the Lord, especially when they gathered in hosts around their God. "When thou marchest out as a camp against thine enemies, beware of every evil thing." What is meant by an "evil thing" is stated in Deuteronomy 23:10-13, viz., uncleanness, and uncleanliness of the body.

Keep from every wicked thing - Then especially take heed, because that is a time of confusion and licentiousness; when the laws of God and man cannot be heard for the noise of arms; because the success of thy arms depends upon God's blessing, which wicked men have no reason to expect; and because thou dost carry thy life in thy hand, and therefore hast need to be well prepared for death and judgment.