לרפואת אסתר רות בת נעמי שרה
A person begins approaching holiness because the soul has shined and achieved a sense of G-dly perfection. This results in a person feeling bitterness due to his sins which make him spiritually weak and limited. But this is the foundation of teshuva done out of love because he yearns to cling and attach himself to his Creator but cannot and feels the pain of the gap between his desires and reality. It is very positive for every person of character to accept this feeling of bitterness with happiness and a good heart, and then this deep pain is transformed into elevated joy into which a steady flow of holy, delicious pleasure will flow.
הַצַּעַר, שֶׁמַּרְגִּישִׁים בְּעֵת שֶׁנִּגָּשִׁים אֶל כָּל דָּבָר שֶׁבִּקְדֻשָּׁה, הֲרֵי הוּא בָּא מִתּוֹךְ שֶׁאָז הַנְּשָׁמָה הִיא מְאִירָה יוֹתֵר וּמִתְגַּלֶּה בָּהּ הַתֹּכֶן שֶׁל הַשְּׁלֵמוּת הַמֻּחְלָטָה, וְהִיא רוֹאָה מִתּוֹךְ כָּךְ אֶת הָאַפְסִיּוּת שֶׁבְּהַגְבָּלָתָהּ וְצִמְצוּמָהּ, וְהִיא מִתְמַרְמֶרֶת עַל כָּל מַה שֶּׁגּוֹרֵם לָהּ עִצּוּר–כֹּחַ וְכֵהוּת. וְזֶה הוּא בֶּאֱמֶת יְסוֹד הַתְּשׁוּבָה מֵאַהֲבָה, שֶׁרָאוּי לְכָל אָדָם בַּעַל נֶפֶשׁ לְקַבֵּל אֶת הַהַרְגָּשָׁה הַמְּרוּרָה הַזֹּאת בְּשִׂמְחָה וְטוּב לֵב, וְאָז עֹמֶק הַצַּעַר הַזֶּה מִתְהַפֵּךְ הוּא לְתֹכֶן שֶׁל עֹנֶג עֶלְיוֹן, שֶׁשִּׁפְעַת עֲדָנִים שֶׁל קֹדֶשׁ מִתְגַּלִּים בּוֹ.
[אורות התשובה ט"ז ה]
The reason that bitterness is transformed into an elevated sense of joy is that the feelings of bitterness and distance themselves create a closeness. Hashem comes close to those who feel pain over being so distant. The pasuk says [Yesahya 57/15] ואת דכא ושפל רוח - Hashem is close to those downtrodden and of a low spirit. So the feelings of depression and anguish over one's sins and consequently, distance from Hashem, engender a renewed closeness. There is nothing like closeness to Hashem to make one happy and fulfilled.
