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.

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.

When the host goeth forth against thine enemies, then keep thee from every wicked thing.

23:9 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.

9-14. 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.

23:9-14 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.