מְאֹד צְרִיכִים לְהִזָּהֵר מִן הָעַצְבוּת, אֲבָל לֹא בְּמִדָּה גְּדוֹלָה כָּזוֹ שֶׁתִּמְנַע אֶת אוֹר הַתְּשׁוּבָה מִלַּחְדֹּר אֶל עֹמֶק הַנְּשָׁמָה, שֶׁאָז הָעַצְבוּת מִתְפַּשֶּׁטֶת הִיא כְּמַחֲלָה מַמְאֶרֶת בְּכָל קְצוֹת הַגּוּף וְהַנֶּפֶשׁ, מִפְּנֵי שֶׁהַחֵטְא מַדְאִיב אֶת הַלֵּב וְגוֹרֵם לָעַצְבוּת לְהִתְאַזְרֵחַ עַל הַמְּרִירוּת הַקּוֹדַחַת שֶׁל תַּבְעֵרַת הַתְּשׁוּבָה, שֶׁאַף עַל פִּי שֶׁיֵּשׁ בָּהּ חֲלָקִים עַצְבָּנִיִּים הֵם כְּאֵשׁ מְטַהֵר, מְצָרְפִים אֶת הַנְּשָׁמָה, מַחֲזִיקִים אוֹתָהּ עַל הַבָּסִיס שֶׁל הַשִּׂמְחָה הַטִּבְעִית הַתְּמִידִית הָרְאוּיָה לָהּ.
[During the process of teshuva] we must be very wary of sadness,
but not so much that it prevents Teshuva-light from penetrating to the depth of the soul,
for then depression spreads like a malignant disease to all corners of the body and soul,
because sin pains the heart, and causes sadness to settle in permanently on top of the feverish bitterness of Teshuva’s fire,
which, while it does have parts that are painful, these are like a purifying fire:
they purify the soul they strengthen her,
and ground her firmly in the natural, constant joy that is fitting for her.
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One of the YESODOS of the teachings of the Rav is to find a balance between different middos - even seemingly "negative" ones. Sadness can be very dangerous if one is overcome by it. But it plays a very important role in the teshuva process if used in the correct amounts. If one is not sad at all about his or her sins then the impurity of the sin will spread like a cancer to all parts of his BODY [!!] and soul. If one is too sad then he or she is paralyzed and serves Hashem lifelessly. The correct path is enough sadness to purify the soul of the contamination of the sin while at the same time continuing to learn Torah and keep mitzvos with simcha gedola!!:-)
