נוהגים בכל מקום להרבו' נרות בבתי כנסיו' ולהציע בגדים נאים בבית הכנסת: הגה... יש שכתבו שנהגו ללבוש בגדים לבנים ונקיים ביוה"כ דוגמת מלאכי השרת וכן נוהגין ללבוש הקיטל שהוא לבן ונקי גם הוא בגד מתים ועי"ז לב האדם נכנע ונשבר:
It is customary in all places to increase the candles in the synagogues and to wear nice clothing in the synagogue...
Remah: There are those who have written that we should wear clean white clothes on Yom Kippur, to make ourselves like the Ministering Angels, and yes it is our custom to wear a kittel, which is white and clean. It is also the clothing of the dead, and because of this it assists in the opening and breaking of the heart.
At first taking the dead out for burial was more difficult for the relatives than the actual death, to the point that relatives would abandon the corpse and run away. Until Rabban Gamliel came and acted with leniency, instructing that the corpse be taken out in linen garments. And the people adopted this practice after him and had themselves taken out in linen garments. Rav Pappa said: And nowadays, all the people follow the practice, even in plain hemp garments that cost only one Zuz.
אמר ליה ריש גלותא לרב המנונא מאי דכתיב ולקדוש ה׳ מכובד אמר ליה זה יום הכפורים שאין בו לא אכילה ולא שתיה אמרה תורה כבדהו בכסות נקיה וכבדתו...
The Exilarch said to Rav Hamnuna: What is the meaning of that which is written, “The holy one of God is honoured” (Isaiah 58:13)? Rav Hamnuna said to him: That is Yom Kippur, when there is no eating or drinking, and so the Torah said: Honour it with a clean garment...
(ח) אָמַר רַבָּן שִׁמְעוֹן בֶּן גַּמְלִיאֵל, לֹא הָיוּ יָמִים טוֹבִים לְיִשְׂרָאֵל כַּחֲמִשָּׁה עָשָׂר בְּאָב וּכְיוֹם הַכִּפּוּרִים, שֶׁבָּהֶן בְּנוֹת יְרוּשָׁלַיִם יוֹצְאוֹת בִּכְלֵי לָבָן שְׁאוּלִין, שֶׁלֹּא לְבַיֵּשׁ אֶת מִי שֶׁאֵין לוֹ. כָּל הַכֵּלִים טְעוּנִין טְבִילָה. וּבְנוֹת יְרוּשָׁלַיִם יוֹצְאוֹת וְחוֹלוֹת בַּכְּרָמִים. וּמֶה הָיוּ אוֹמְרוֹת, בָּחוּר, שָׂא נָא עֵינֶיךָ וּרְאֵה, מָה אַתָּה בוֹרֵר לָךְ. אַל תִּתֵּן עֵינֶיךָ בַנּוֹי, תֵּן עֵינֶיךָ בַמִּשְׁפָּחָה. שֶׁקֶר הַחֵן וְהֶבֶל הַיֹּפִי, אִשָּׁה יִרְאַת ה' הִיא תִתְהַלָּל (משלי לא). וְאוֹמֵר, תְּנוּ לָהּ מִפְּרִי יָדֶיהָ, וִיהַלְלוּהָ בַשְּׁעָרִים מַעֲשֶׂיהָ...
(8) Rabbi Shimon ben Gamaliel said: There were no days of joy in Israel greater than the fifteenth of Av and Yom Kippur. On these days the daughters of Jerusalem would go out in borrowed white garments in order not to shame any one who had none. All these garments required immersion. The daughters of Jerusalem come out and dance in the vineyards. What would they say? Young man, lift up your eyes and see what you choose for yourself. Do not set your eyes on beauty but set your eyes on the family. “Grace is deceitful, and beauty is vain, but a woman that fears the Lord, she shall be praised” (Proverbs 31:30). And it further says, “Give her of the fruit of her hands; and let her works praise her in the gates” (ibid, 31:31)...
"Shrouds are made without pockets"
-Yiddish proverb