איש איש כי תשטה אשתו. מַה כָּתוּב לְמַעְלָה מִן הָעִנְיָן? "וְאִישׁ אֶת קֳדָשָׁיו לוֹ יִהְיוּ", אִם אַתָּה מְעַכֵּב מַתְּנוֹת הַכֹּהֵן, חַיֶּיךָ שֶׁתִּצְטָרֵךְ לָבֹא אֶצְלוֹ לְהָבִיא לוֹ אֶת הַסּוֹטָה: איש איש כי תשטה אשתו IF ANY MAN’S WIFE GO ASIDE [AND ACT DECEITFULLY AGAINST HIM] — What is stated above, immediately before this section? ואיש את קדשיו לו יהיו: If you withhold the gifts due to the priest (cf. Rashi on v. 10), by your life, you will have to come to him in order to bring him your faithless wife for the ordeal by the waters (Berakhot 63a). (The translation therefore is: “A man who remains with his holy things, not giving them to the priest, לו יהיו they — the man and his wife — will become subject to him [require his services])”.
איש איש. לְלַמֶּדְךָ שֶׁמּוֹעֶלֶת בִּשְׁתַּיִם – בְּאִישׁ מִלְחָמָה שֶׁלְּמַעְלָה, וְאִישָׁהּ מִלְּמַטָּה: איש איש — The double expression איש איש is employed to teach you that she (the faithless wife) deals treacherously in two respects — against Him above Who bears the appelation of איש, as in the text "[the Lord is] a Man of the war” (Exodus 15:3), and against her husband (אישה) here below (Midrash Tanchuma, Vaetchanan 5).
כי תשטה אשתו. שָׁנוּ רַבּוֹתֵינוּ אֵין הַמְנָאֲפִין נוֹאֲפִין עַד שֶׁתִּכָּנֵס בָּהֶן רוּחַ שְׁטוּת, דִּכְתִיב "כִּי תִשְׂטֶה" וְכָתוּב בּוֹ "נֹאֵף אִשָּׁה חֲסַר לֵב" (משלי ו'); וּפְשׁוּטוֹ שֶׁל מִקְרָא: כי תשטה — תֵּט מִדַּרְכֵי צְנִיעוּת וְתֵחָשֵׁד בְּעֵינָיו, כְּמוֹ "שְׂטֵה מֵעָלָיו וַעֲבֹר" (שם ד'), "אַל יֵשְׂטְ אֶל דְּרָכֶיהָ לִבֶּךָ" (שם ז'): כי תשטה — Our Rabbis have taught (Midrash Tanchuma, Nasso 5): “Adulterers do never sin until a spirit of madness enters into them”, as it written, of her כי תשטה “if she becomes mad” (taking תִשְׂטֶה in the sense of תִשְׂטֶה, i.e. to become a שׁוֹטֶה, and so, too, of him Scripture writes, (Proverbs 6:32) “Whoso committeth adultery with a woman lacketh understanding”. — But the plain sense of the verse is that כי תשטה means: if she deviates from the path of modesty and thereby becomes suspect in his eyes. The word is similar to, (Proverbs 4:15) “turn away (שְׂטֵה) from it, and pass by”; (Proverbs 7:25) “Let not your heart turn (יַשְׂטְ) to her ways”.
ומעלה בו מעל. וּמַהוּ הַמַּעַל? ושכב איש אתה: ומעלה בו מעל AND SHE ACTS UNFAITHFULLY AGAINST HIM — Wherein consists this infidelity? ושכב איש אתה THAT A MAN LIETH WITH HER.