Our Mishna on Amud Beis uses an unusual form, instead of saying  הֲרֵי אַתְּה עָלַי חֵרֶם behold you (“atah” masculine) are cherem, it says הֲרֵי אַתְּ behold you (”at” female), though the Mishna is referring to an interchange between two men, as it gives no indication of a gender specific halakha. 

Tosafos Yom Tov notes this and remarks that occasionally Hebrew will use the word form “at” instead of “atah” but it can still be male. He brings a verse in Yechezkel (28:14) that also uses the feminine form of “at” even when addressing a male. There are two notable pesukim in Torah that use את “at” even in regard to a male, and there is a common thread:

Bamidbar (11:13) 

וְאִם־כָּ֣כָה ׀ אַתְּ־עֹ֣שֶׂה לִּ֗י הׇרְגֵ֤נִי נָא֙ הָרֹ֔ג אִם־מָצָ֥אתִי חֵ֖ן בְּעֵינֶ֑יךָ וְאַל־אֶרְאֶ֖ה בְּרָעָתִֽי׃

If You would deal thus with me, kill me rather, I beg You, and let me see no more of my wretchedness!”

And, Devarim (5:24)

קְרַ֤ב אַתָּה֙ וּֽשְׁמָ֔ע אֵ֛ת כׇּל־אֲשֶׁ֥ר יֹאמַ֖ר ה׳ אלקינו וְאַ֣תְּ ׀ תְּדַבֵּ֣ר אֵלֵ֗ינוּ אֵת֩ כׇּל־אֲשֶׁ֨ר יְדַבֵּ֜ר ה׳ אלקינו אֵלֶ֖יךָ וְשָׁמַ֥עְנוּ וְעָשִֽׂינוּ׃

You go closer and hear all that our God Hashem says, and then you tell us everything that our God Hashem tells you, and we will willingly do it.

In both places, Rashi notes that it is said in the feminine form to hint that Moshe became weakened (hinted at by the use of the feminine word form) and lost spiritual vigor. This loss was due to a weakening of the Jewish people’s spiritual resolve. The leader is only as strong as his people.

In general, one of the fascinating features of Hebrew is that the word form can change from masculine to feminine based on the metaphorical subject matter and not just the individual speaking. (This can also be seen from Gemara Kiddushin 2 where the word derech can be feminine or masculine depending on what is the subject under discussion.)

Ramban in Bamidbar (ibid) has difficulty with this interpretation of Rashi. The problem is, that if one looks at the verse itself, in this case the subject matter is God. So even if Moshe meant to say that he was weakened as a woman, It doesn’t fit well because he is not talking about himself; he is rather addressing God.

Ramban says the feminine form is hinting at the idea that Middas Hadin(Divine Attribute of Justice) has become aroused. I’m not sure how the feminine form hints at that, unless we understand there is a kind of Tigress-like reaction, that is the female species can be more fierce when protecting their cubs. Or, as I’ve seen Ramban explained in the Sefaria translation, the word Middah itself is female, so the verse is hinting at Middah for the subject matter.

An easy answer for Rashi is that Moshe was speaking out of deference, and really was referring to Hashem as being, so to speak, weakened. How is this possible? This is based on the mystical idea that Hashem can only be as powerful in this world, as humans allow his presence to manifest itself.

As the Gemara Berachos (5b) says:

שֶׁגּוֹרֵם לַשְּׁכִינָה שֶׁתִּסְתַּלֵּק מִיִּשְׂרָאֵל, שֶׁנֶּאֱמַר: ״וְיֶעְתַּק צוּר מִמְקֹמוֹ״. וְאֵין ״צוּר״ אֶלָּא הַקָּדוֹשׁ בָּרוּךְ הוּא, שֶׁנֶּאֱמַר: צוּר יְלָדְךָ תֶּשִׁי״.

It causes the Divine Presence to remove itself from Israel, as it is stated in the continuation of the verse: “The Rock will be moved from its place.” The rock, God, is forced to remove His presence. And Rock means nothing other than the Holy One, Blessed be He, as it is stated: “Of the Rock that gave birth to you, you have been unmindful, and you have forgotten God Who bore you” 

This is somewhat indirect. However, Eichah Rabbah (1:33) states it explicitly 

רַבִּי עֲזַרְיָה בְּשֵׁם רַבִּי יְהוּדָה בְּרַבִּי סִימוֹן אָמַר בִּזְּמַן שֶׁיִּשְׂרָאֵל עוֹשִׂין רְצוֹנוֹ שֶׁל מָקוֹם מוֹסִיפִין כֹּחַ בִּגְּבוּרָה שֶׁל מַעְלָה, כְּמָה דְאַתְּ אָמַר (תהלים ס, יד): בֵּאלֹהִים נַעֲשֶׂה חָיִל. וּבִזְּמַן שֶׁאֵין יִשְׂרָאֵל עוֹשִׂין רְצוֹנוֹ שֶׁל מָקוֹם, כִּבְיָכוֹל מַתִּישִׁין כֹּחַ גָּדוֹל שֶׁל מַעְלָן, דִּכְתִיב (דברים לב, יח): צוּר יְלָדְךָ תֶּשִּׁי. רַבִּי יְהוּדָה בְּרַבִּי סִימוֹן בְּשֵׁם רַבִּי לֵוִי בְּרַבִּי טַרְפוֹן בִּזְּמַן שֶׁיִּשְׂרָאֵל עוֹשִׂין רְצוֹנוֹ שֶׁל הַקָּדוֹשׁ בָּרוּךְ הוּא, מוֹסִיפִין כֹּחַ בִּגְּבוּרָה שֶׁל מַעְלָה, כְּמָה דְאַתְּ אָמַר (במדבר יד, יז): וְעַתָּה יִגְדַל נָא כֹּחַ ה'. וּבִזְמַן שֶׁאֵין עוֹשִׂין רְצוֹנוֹ שֶׁל הַקָּדוֹשׁ בָּרוּךְ הוּא, כִּבְיָכוֹל, מַתִּישִׁין כֹּחַ גָּדוֹל שֶׁל מַעְלָן, וְהוֹלְכִין גַּם הֵם בְלֹא כֹחַ לִפְנֵי רוֹדֵף. 

Rabbi Azarya said in the name of Rabbi Yehuda ben Rabbi Simon: When Israel performs the will of the Omnipresent, they add strength to the power on high, just as it says: “With God we will triumph” (Psalms 60:14). When Israel does not perform the will of the Omnipresent, they, as it were, exhaust the great power on high, as it is written: “You abandoned the Rock that begot you” (Deuteronomy 32:18). Rabbi Yehuda ben Rabbi Simon [said] in the name of Rabbi Levi ben Rabbi Tarfon: When Israel performs the will of the Holy One blessed be He, they add strength to the power on high, just as it says: “Now, please, let the power of the Lord be great” (Numbers 14:17). When Israel does not perform the will of the Holy One blessed be He, they, as it were, exhaust the great power on high, and they, too, go “powerless before the pursuer.”

It is a remarkable idea in Judaism that we are empowered with the ability to energize or de-energize God’s presence in the world. This is related to the idea we saw in Psychology of the Daf Nedarim 8.