where even treif is kosher

1) I've been swamped with work, but wanted to get in something on the parsha and share a beautiful thought of Rav Kook.  Ramban on our parsha explains why the Torah speaks about kashering and toiveling the klei Midyan but did not speak about doing the same for the kelim taken during the war with Sichon and Og:

והזהיר אותם עתה בהגעלת כלי מדין מאיסורי הגוים, ולא אמר להם זה מתחלה בכלי סיחון ועוג שלקחו גם הם שללם, כמו שאמר: רק הבהמה בזזנו לנו ושלל הערים אשר לכדנו (דברים ב׳:ל״ה). והטעם: כי סיחון ועוג מלכי האמורי הם וארצם מנחלת ישראל היא, והותר להם כל שללם אפילו האיסורין, דכתיב: ובתים מלאים כל טוב אשר לא מלאת (דברים ו׳:י״א), ואמרו רבותינו (בבלי חולין י״ז.): קתליג דחזירי אישתרי להו. אבל מדין לא היה משלהם, ולא לקחו את ארצם, רק לנקום נקמתם הרגו אותם ולקחו שללם, ולכך נהג האיסור בכליהם. וכן בדין הטומאה שהזהירם עתה: ואתם חנו מחוץ למחנה שבעת ימים וגו׳ (במדבר ל״א:י״ט), כי במלחמת סיחון ועוג היו כל ישראל, וטומאה הותרה בצבור. ועל דרך הפשט הזהירם: ואתם חנו מחוץ למחנה שבעת ימים ותתחטאו (במדבר ל״א:י״ט) – כדי שלא יטמאו את העם, אבל שם כולם היו שוים בדבר.

Ramban holds that during battle for the territory of Sichon v'Og, which was part of Eretz Yisrael, the rules of kashrus were suspended. This is a special din learned out from Devarim 6:11 that promises וּבָ֨תִּ֜ים מְלֵאִ֣ים כׇּל־טוּב֮ אֲשֶׁ֣ר לֹא־מִלֵּ֒אתָ֒ וּבֹרֹ֤ת חֲצוּבִים֙ אֲשֶׁ֣ר לֹא־חָצַ֔בְתָּ כְּרָמִ֥ים וְזֵיתִ֖ים אֲשֶׁ֣ר לֹא־נָטָ֑עְתָּ וְאָכַלְתָּ֖ וְשָׂבָֽעְתָּ that one is allowed to enjoy the spoils of a war of conquest in Eretz Yisrael, whether kosher or trief.  The battle against Midyan was not a battle of conquest for territory in Eretz Yisrael, and therefore the Torah needs to speak about how to treat the treif kelim. 

I saw Rav Kook quoted as saying the following hesber: We translate "assur" as meaning "prohibited," but that's not exactly right.  Assur means tied up, locked up.  A beis ha'assurim is a prison.  The Baal haTanya explains that when we eat and have strength to learn and daven, there is a release of spiritual as well as physical energy from the food we consume.  In food which is assur, that energy is locked up; it cannot be liberated and released for good, and so the food is off limits.  However, says Rav Kook, when a Jewish soldier puts his life on the line fighting for Eretz Yisrael, then even though under usual circumstances he cannot elevate that bacon or that cheeseburger for avodas Hashem, when he is engaged in kibush ha'aretz he is on such a high level that he is able to do so.  The drive to take Eretz Yisrael gives us strength to accomplish things in ruchniyus that otherwise we would be unable to achieve.

(The Rambam, parenthetically, has a completely different understanding of this din.  He puts it in the same chapter (Melachim 8:1) as his discussion of the laws of yefat toar (see Avi Ezri) and learns that the heter to eat treif is a special dispensation 1) only for soldiers, and it  2) applies both to milchemes reshus and milchemes mitzvah, whether fighting to conquer the 7 nations in Eretz Yisrael or fighting some other war.  

Why then does the Torah mention kashering kelim here?  About 10 years ago we discussed the Rogatchover's chiddush that the fight against Midyan did not have a din milchama, but was an act of nekama.  "Nikom mikmas Bnei Yisrael..."  )

2) The Netziv takes note of an interesting repitition in Moshe's recounting to the tribes of Reuvain,Gad, and Menashe the sin of the mergalim and the previous generation:

Pesukim 10-11:

 וַיִּֽחַר־אַ֥ף ה׳ בַּיּ֣וֹם הַה֑וּא וַיִּשָּׁבַ֖ע לֵאמֹֽר

 אִם־יִרְא֨וּ הָאֲנָשִׁ֜ים הָעֹלִ֣ים מִמִּצְרַ֗יִם מִבֶּ֨ן עֶשְׂרִ֤ים שָׁנָה֙ וָמַ֔עְלָה אֵ֚ת הָאֲדָמָ֔ה אֲשֶׁ֥ר נִשְׁבַּ֛עְתִּי לְאַבְרָהָ֥ם לְיִצְחָ֖ק וּֽלְיַעֲקֹ֑ב כִּ֥י לֹא־מִלְא֖וּ אַחֲרָֽי

Pasuk 13:

וַיִּֽחַר־אַ֤ף ה׳ בְּיִשְׂרָאֵ֔ל וַיְנִעֵם֙ בַּמִּדְבָּ֔ר אַרְבָּעִ֖ים שָׁנָ֑ה עַד־תֹּם֙ כׇּל־הַדּ֔וֹר הָעֹשֶׂ֥ה הָרַ֖ע בְּעֵינֵ֥י ה׳

Why "va'yichar af Hashem..." two times in speaking about the same event?  

The sin of the meraglim was in fact a double-sin.  Eretz Yisrael is not just some random piece of real estate that Hashem designated to be our homeland.  Eretz Yisrael is the makom hashra'as ha'Shechina.  To live in Eretz Yisrael is to live under direct hashgacha, which is a tremendous privilege, but also a tremendous responsibility.  כִּ֥י לֹא־מִלְא֖וּ אַחֲרָֽי means the sin of the meraglim was not just in rejecting Eretz Yisrael -- it was rejecting the Shechina.  "The meraglim didn't want to be there because I am there," said Hashem.  "It's me they can't live with, not just the country that they don't like."

Nachamu nachamu ami...  A double-nechama.  We don't just want to return to the land; we want to be there and live in Hashem's presence, with a hashra'as haShechina.