No sword shall pass

In parashat Bechukotai, we discover that if you follow Hashem's statutes, then:

6. And I will grant peace in the Land, and you will lie down with no one to frighten [you]; I will remove wild beasts from the Land, and no army will pass through your land;

ו. וְנָתַתִּי שָׁלוֹם בָּאָרֶץ וּשְׁכַבְתֶּם וְאֵין מַחֲרִיד וְהִשְׁבַּתִּי חַיָּה רָעָה מִן הָאָרֶץ וְחֶרֶב לֹא תַעֲבֹר בְּאַרְצְכֶם:

Rashi on that pasuk:

and no army will pass through your land: It is unnecessary to state that they will not come to wage war, but [they will not come] even to pass through your land from one country to another. — [Torath Kohanim 26:9]

וחרב לא תעבר בארצכם: אין צריך לומר שלא יבאו למלחמה, אלא אפילו לעבור דרך ארצכם ממדינה למדינה:

This is a midrash on the pasuk. On a peshat level, this expression of וְחֶרֶב לֹא תַעֲבֹר בְּאַרְצְכֶם might simply be an idiomatic expression indicating peace, or lack of invasion by an opposing army. But midrashically, it does not (merely) say that there will be no attack from the army, but uses even the more neutral idea that the sword will not pass. This indicates that even for peaceful (toward your country, at least) purposes they will not pass.

The midrash in Torat Kohanim which Rashi draws this from makes explicit mention of the role this derasha played in the time of Yoshiyahu:

וחרב לא תעבור בארצכם. אין צ״ל שלא יהו באים עליכם למלחמה אלא שלא

יהו העוברים והשבים עוברים ממדינה לתבירתה כדרך שעברו בימי יאשיהו.

In Taanis 22b, we see this derasha coupled with the story of Yoshiyahu

אמר ר' שמואל בר נחמני אמר רבי (יוחנן) מפני מה נענש יאשיהו מפני שהיה לו לימלך בירמיהו ולא נמלך מאי דרש  (ויקרא כו, ו) וחרב לא תעבור בארצכם מאי חרב אילימא חרב שאינה של שלום והכתיב ונתתי שלום בארץ אלא אפילו של שלום והוא אינו יודע שאין דורו דומה יפה

He made this derasha based on the fact that earlier, at the start of the pasuk, there was a promise of וְנָתַתִּי שָׁלוֹם בָּאָרֶץ,  "And I will grant peace in the Land". If so, the statement about no sword passing through is obvious. If it comes to teach something new, it must be that even the sword of peace shall not pass. Yet, he Yoshiyahu did not realize that this promise was not for his generation, because they were not of a sufficient level. And so, he should have consulted with Yirmeyahu, who could have informed him of this. This error resulted in Yoshiyahu's death, when he refused to allow Pharaoh Necho's army peaceful passage through the land on the way to fight against Carkemish. (See Divrei Hayamim II 35:20.)

Thus, despite King Yoshiyahu's error in application, they derasha itself stands as a correct derasha.

This might serve as good lesson to many of us, nowadays. We see a pasuk, we see a derasha, we see a gemara, and we think we understand it. And maybe we do, and that is good talmud Torah, whether or not we understand it correctly. But then we seek to apply it to the actual world, to what should be done, religiously, personally, politically. It is very easy to justify almost any conclusion, when one interprets sources. And even if the conclusion is justified, it is not necessarily justified for the present situation, whatever the present situation might be.

Now, while these close readings make for good derash, they do not make for good peshat, IMHO. As noted above, we may view "pass through the land" as an idiomatic expression. And as to the unnecessary duplication, we might view it as a strengthening for poetic effect.

Ralbag makes an interesting statement as to what benefit they would get from this cherev shel shalom not passing through the land. He writes that this indicates even a sword of peace, for it is already possible that damage and fear will result to the residents of the land, as is made well known from the matter of Yoshiyahu, when Pharaoh Necho and his army passed through the land of Israel.

This strikes me as a somewhat strange comment, for the damage was only done because Yoshitahu didn't let the sword pass peacefully through his land.

But indeed, not having strange armies pass through your land on the way to battle is something that people of a country might like. Furthermore, not letting an army through your landspace indicates that you are a sovereign power, and people can't simply traipse through your land against your will.