The Alter Rebbe explains how a broken heart can be transformed into active divine service, turning spiritual weakness into renewed effort. This is helpful for understanding the avodah of a fast day as inner refinement and recommitment.
וְלָזֹאת, צָרִיךְ לְבַטְּשָׁהּ וּלְהַשְׁפִּילָהּ לֶעָפָר, דְּהַיְינוּ, לִקְבּוֹעַ עִתִּים לְהַשְׁפִּיל עַצְמוֹ, לִהְיוֹת ״נִבְזֶה בְעֵינָיו נִמְאָס״, כַּכָּתוּב, וְ״לֵב נִשְׁבָּר״ – ״רוּחַ נִשְׁבָּרָה״, הִיא הַסִּטְרָא אָחֳרָא, שֶׁהִיא הִיא הָאָדָם עַצְמוֹ בַּבֵּינוֹנִים, שֶׁנֶּפֶשׁ הַחִיּוּנִית הַמְחַיָּה הַגּוּף, הִיא בְּתָקְפָּהּ כְּתוֹלַדְתָּהּ בְּלִבּוֹ, נִמְצָא – הִיא הִיא הָאָדָם עַצְמוֹ. וְהִנֵּה, כָּל מַה שֶּׁיַּאֲרִיךְ בְּעִנְיָינִים אֵלּוּ בְּמַחֲשַׁבְתּוֹ וְגַם בְּעִיּוּנוֹ בִּסְפָרִים, לִהְיוֹת לִבּוֹ נִשְׁבָּר בְּקִרְבּוֹ, וְ״נִבְזֶה בְעֵינָיו נִמְאָס״ כַּכָּתוּב, בְּתַכְלִית הַמִּיאוּס, וּלְמָאֵס חַיָּיו מַמָּשׁ, הֲרֵי בָּזֶה מְמָאֵס וּמְבַזֶּה הַסִּטְרָא אָחֳרָא וּמַשְׁפִּילָהּ לֶעָפָר, וּמוֹרִידָהּ מִגְּדוּלָּתָהּ וְגַסּוּת רוּחָהּ וְגַבְהוּתָהּ, שֶׁמַּגְבִּיהַּ אֶת עַצְמָהּ עַל אוֹר קְדוּשַּׁת נֶפֶשׁ הָאֱלֹהִית לְהַחֲשִׁיךְ אוֹרָהּ. וְגַם, יַרְעִים עָלֶיהָ בְּקוֹל רַעַשׁ וְרוֹגֶז לְהַשְׁפִּילָהּ, כְּמַאֲמַר רַבּוֹתֵינוּ־זִכְרוֹנָם־לִבְרָכָה: ״לְעוֹלָם יַרְגִּיז אָדָם יֵצֶר טוֹב עַל יֵצֶר הָרָע, שֶׁנֶּאֱמַר: רִגְזוּ וְגוֹ׳״, דְּהַיְינוּ, לִרְגּוֹז עַל נֶפֶשׁ הַבַּהֲמִית, שֶׁהִיא יִצְרוֹ הָרָע, בְּקוֹל רַעַשׁ וְרוֹגֶז בְּמַחֲשַׁבְתּוֹ, לוֹמַר לוֹ: ״אַתָּה רָע וְרָשָׁע וּמְשׁוּקָּץ וּמְתוֹעָב וּמְנֻוָּול וְכוּ׳ – כְּכָל הַשֵּׁמוֹת שֶׁקָּרְאוּ לוֹ חֲכָמֵינוּ־זִכְרוֹנָם־לִבְרָכָה – בֶּאֱמֶת; עַד מָתַי תַּסְתִּיר לִפְנֵי אוֹר־אֵין־סוֹף בָּרוּךְ־הוּא, הַמְמַלֵּא כָּל עָלְמִין, הָיָה הֹוֶה וְיִהְיֶה בְּשָׁוֶה, גַּם בְּמָקוֹם זֶה שֶׁאֲנִי עָלָיו, כְּמוֹ שֶׁהָיָה אוֹר אֵין־סוֹף בָּרוּךְ־הוּא לְבַדּוֹ קוֹדֶם שֶׁנִּבְרָא הָעוֹלָם, בְּלִי שׁוּם שִׁינּוּי, כְּמוֹ שֶׁכָּתוּב: ״אֲנִי ה׳ לֹא שָׁנִיתִי״, כִּי הוּא לְמַעְלָה מֵהַזְּמַן וְכוּ׳, וְאַתָּה מְנֻוָּול וְכוּ׳, מַכְחִישׁ הָאֱמֶת הַנִּרְאֶה לָעֵינַיִם, דְּכוּלָּא קַמֵּיהּ כְּלָא מַמָּשׁ בֶּאֱמֶת, בִּבְחִינַת רְאִיָּיה חוּשִׁיִּית״. וְהִנֵּה, עַל יְדֵי זֶה יוֹעִיל לְנַפְשׁוֹ הָאֱלֹהִית, לְהָאִיר עֵינֶיהָ בֶּאֱמֶת יִחוּד אוֹר־אֵין־סוֹף בִּרְאִיָּה חוּשִׁיִּית, וְלֹא בְּחִינַת שְׁמִיעָה וַהֲבָנָה לְבַדָּהּ, כְּמוֹ שֶׁנִּתְבָּאֵר בְּמָקוֹם אַחֵר, שֶׁזֶּהוּ שֹׁרֶשׁ כָּל הָעֲבוֹדָה.
Therefore one must crush it and cast it down to the ground, that is to say, by setting aside appointed times for humbling oneself and considering oneself despicable and contemptible, as is written, “A broken heart, a broken spirit”—this is the sitra achara, which is the very man himself in benonim (intermediates), in whose heart the vital soul which animates the body is in its native strength; hence it is the very man himself. The longer he will reflect on these matters in his thoughts, delving deeply also into books, in order to break down his heart within him and render himself shamed and despised in his own eyes, as is written in the Scriptures, so utterly despised that he despises his very life—the more he despises and degrades thereby the sitra achara, casting it down to the ground and humbling it from its haughtiness and pride and self-exaltation, wherewith it exalts itself over the light of the holiness of the divine soul, obscuring its effulgence. He must also thunder against it with a strong and raging voice in order to humble it, as the Rabbis state, “A person should always rouse the good impulse against the evil impulse, as it is written, ‘Rage, and do not sin.’” That is to say, one must rage against the animal soul, which is his evil impulse, with stormy indignation in his mind, saying to it: “You are truly evil and wicked, abominable, loathsome, and disgraceful,” and likewise with all the epithets by which our Sages, of blessed memory, have called it, “How long will you conceal the light of the En Sof, blessed is He, which pervades all the worlds; which was, is, and will be the same, including also this place where I stand, just as the light of the En Sof, blessed is He, was alone before the world was created, without any change, as is written, ‘For I, the L–rd, have not changed,’ for He transcends time, and so forth? But you, who are repulsive, and so forth, deny the truth, which is plain to see, by physical sight, that everything in His presence is truly like nothing at all.” In this way he will help his divine soul to enlighten her eyes with the truth of the unity of the light of the En Sof with a perceptive vision and not merely by cognition alone, as it were, as is explained elsewhere that this is the core of the whole [Divine] service.