Kommentar zu Dewarim 23:10

כי תצא וגו׳ ונשמרת WHEN [THE HOST] GOETH FORTH [AGAINST THINE ENEMIES], THEN KEEP THEE [FROM EVERY EVIL THING] — because Satan accuses men in time of danger (Jerusalem Talmud Shabbat 2:6; Midrash Tanchuma, Vayigash 1 on Genesis 42:4; cf. Rashi on that verse and our Note thereon).

WHEN THOU GOEST FORTH IN CAMP AGAINST THINE ENEMIES, THEN THOU SHALT KEEP THEE FROM EVERY EVIL — “because Satan indicts [people] in the hour of danger.” This is Rashi’s language.
The correct interpretation regarding this commandment appears to me that Scripture is warning of a time when sin is rampant. The well-known custom of forces going to war is that they eat all abominable things, rob and plunder, and are not ashamed even of lewdness and all vileness. The fairest of man by nature comes to be possessed of cruelty and fury when the army advances against the enemy. Therefore, Scripture warned, then thou shalt keep thee from every evil. And by way of the simple meaning of Scripture this is an admonition against doing anything forbidden. And in the Sifre it is stated:²⁷¹Sifre, Ki Theitzei 254. “I might think that Scripture is speaking of the laws of defilements and purities and tithes. It therefore says ‘ervah’ [an unseemly thing, which refers to unchastity].²⁷²Further, Verse 15: and that He see no ‘unseemly thing’ in thee. Whence do I know to include idolatry, lewdness,²⁷³“Lewdness.” In our Sifre this term is not mentioned here, and rightly so, since it has already been expressly forbidden, as explained above. bloodshed, and blasphemy? Scripture therefore says, then thou shalt keep thee from every evil. Or perhaps the verse is speaking of defilements and purities, and tithes? It says ervah (an unseemly thing):²⁷²Further, Verse 15: and that He see no ‘unseemly thing’ in thee. just as ervah uniquely represents a deed for which the Canaanites were driven from the Land²⁷⁴Leviticus 18:24. and which removes the Divine Presence [from Israel], so all deeds for which the Canaanites were driven from the Land and which remove the Divine Presence [from Israel] are included in the admonition of this verse. When Scripture states davar [thing, but literally ‘word’ — then thou shalt keep thee from every evil ‘davar’] it includes also ‘evil talk.’” This also is included in the purport of the verse we have explained, that besides the [specific] admonitions which are stated concerning these stringent sins, he added yet a [special] prohibition to an army that we guard against any of these sins so that the Divine Presence withdraw not from the Israelites who are there, just as he said, For the Eternal thy G-d walketh in the midst of thy camp²⁷⁵Further, Verse 15. Thus he who commits any of the great sins while in the army, those about which it is written, they have set their detestable things in the house whereon My Name is called to defile it,²⁷⁶Jeremiah 7:30. [he causes the Divine Presence to withdraw from Israel]. Moreover, [we are to avoid these sins] in order that the enemy should not overpower us because of our committing the very deeds that cause them to be driven from before us, this being the sense of the expression, and to give up thine enemies before thee.²⁷⁵Further, Verse 15. The Sages [in the Sifre] added evil talk [as derived from this admonition] in order that contention should not increase among them and smite them with a very great plague, [even] more than the enemy [will inflict upon them].

כי תצא מחנה על איביך, "When a camp goes out against your enemies, etc." The Torah means that although there are nuances of transgressions which G'd does not go out His way to punish you for, and even if He does decide to punish you the punishment is very mild, the Torah informs us that at a time when there is general danger, such as when one goes out to war, one needs to be careful not to become guilty of violating even the smallest detail of G'd's commandments, i.e. מכל דבר רע, "from anything which is evil." The word דבר includes even causes which bring about evil. The Torah follows this up with the example of a soldier who became ritually unclean due to an involuntary nocturnal seminal emission. Our sages in Ketuvot 46 explain that sexual fantasies one has during the day often are the cause of such emissions during one's sleep. The reason the Torah wrote these two veרses next to one another is to warn us not to entertain such fantasies during the day so that we would not become defiled during the night.