(ט) הָאוֹמֵר, אֶחֱטָא וְאָשׁוּב, אֶחֱטָא וְאָשׁוּב, אֵין מַסְפִּיקִין בְּיָדוֹ לַעֲשׂוֹת תְּשׁוּבָה. אֶחֱטָא וְיוֹם הַכִּפּוּרִים מְכַפֵּר, אֵין יוֹם הַכִּפּוּרִים מְכַפֵּר. עֲבֵרוֹת שֶׁבֵּין אָדָם לַמָּקוֹם, יוֹם הַכִּפּוּרִים מְכַפֵּר. עֲבֵרוֹת שֶׁבֵּין אָדָם לַחֲבֵרוֹ, אֵין יוֹם הַכִּפּוּרִים מְכַפֵּר, עַד שֶׁיְּרַצֶּה אֶת חֲבֵרוֹ. אֶת זוֹ דָּרַשׁ רַבִּי אֶלְעָזָר בֶּן עֲזַרְיָה, מִכֹּל חַטֹּאתֵיכֶם לִפְנֵי יְיָ תִּטְהָרוּ (ויקרא טז), עֲבֵרוֹת שֶׁבֵּין אָדָם לַמָּקוֹם, יוֹם הַכִּפּוּרִים מְכַפֵּר. עֲבֵרוֹת שֶׁבֵּין אָדָם לַחֲבֵרוֹ, אֵין יוֹם הַכִּפּוּרִים מְכַפֵּר, עַד שֶׁיְּרַצֶּה אֶת חֲבֵרוֹ. אָמַר רַבִּי עֲקִיבָא, אַשְׁרֵיכֶם יִשְׂרָאֵל, לִפְנֵי מִי אַתֶּם מִטַּהֲרִין, וּמִי מְטַהֵר אֶתְכֶם, אֲבִיכֶם שֶׁבַּשָּׁמַיִם, שֶׁנֶּאֱמַר (יחזקאל לו), וְזָרַקְתִּי עֲלֵיכֶם מַיִם טְהוֹרִים וּטְהַרְתֶּם. וְאוֹמֵר (ירמיה יז), מִקְוֵה יִשְׂרָאֵל יְיָ, מַה מִּקְוֶה מְטַהֵר אֶת הַטְּמֵאִים, אַף הַקָּדוֹשׁ בָּרוּךְ הוּא מְטַהֵר אֶת יִשְׂרָאֵל:
(9) One who says, "I will sin, and then repent, I will sin [again], and then repent," will not receive an opportunity to repent; [for one who says] "I will sin, and Yom Kipur will atone," Yom Kippur will not atone. Yom Kippur atones for transgressions between a person and God, but for a transgression against one's neighbor, Yom Kipur cannot atone, until he appeases his neighbor. Thus R. Eleazar ben Azariah expounds the text, "From all your sins before the Lord shall ye be clean": For transgressions between a person and God, Yom Kippur atones, for transgressions against one's neighbor, Yom Kippur cannot atone, until he appeases his neighbor. R. Akiva says, Happy are you, Israel! Before whom are you purified, and who purifies you [of your transgressions]? Your Father Who is in heaven. For it is said, "Then will I sprinkle clean water upon you, and ye shall be clean"; and it is also said, "The ritual bath [lit. Hope] of Israel is the Lord"; even as a ritual bath purifies the unclean, so does the Holy One, Blessed be He, purify Israel.
(ז) אַף עַל פִּי שֶׁהוּא נוֹתֵן לוֹ, אֵין נִמְחָל לוֹ עַד שֶׁיְּבַקֵּשׁ מִמֶּנּוּ, שֶׁנֶּאֱמַר (בראשית כ) וְעַתָּה הָשֵׁב אֵשֶׁת וְגוֹ'...
Even when he gives him [the payment], he will not be forgiven until he seeks it [pardon] from him, as it says, "Therefore, restore [Abraham's] wife[—he is a prophet and will intercede for you]" (Genesis 20:7).
רב הוה ליה מילתא בהדי ההוא טבחא לא אתא לקמיה במעלי יומא דכפורי אמר איהו איזיל אנא ' לפיוסי ליה פגע ביה רב הונא אמר ליה להיכא קא אזיל מר אמר ליה לפיוסי לפלניא אמר אזיל אבא למיקטל נפשא אזל וקם עילויה הוה יתיב וקא פלי רישא דלי עיניה וחזייה אמר ליה אבא את זיל לית לי מילתא בהדך בהדי דקא פלי רישא אישתמיט גרמא ומחייה בקועיה וקטליה
[Transgressions between a person and God, etc.]...
... Rav once had a grievance with a certain butcher. The butcher did not come before him (to reconcile). On the eve of Yom Kippur he (Rav) said: "I will go to appease him." Rav Huna met him and asked him: "Where are you going, Master?" He said: "To appease so-and-so." He (Rav Huna) said (to himself): "Abba is about to cause someone's death." Rav came and stood over the butcher, who was sitting and chopping (an animal's) head. He raised his eyes and said to him: "You're Abba!? I have no grievance with you." (Also possibly: "I will have nothing to do with you.") While he was chopping the head, a bone flew off, struck him in the throat, and killed him.
(ח) בַּעֲלֵי תְּשׁוּבָה דַּרְכָּן לִהְיוֹת שְׁפָלִים וַעֲנָוִים בְּיוֹתֵר. אִם חֵרְפוּ אוֹתָן הַכְּסִילִים בְּמַעֲשֵׂיהֶם הָרִאשׁוֹנִים וְאָמְרוּ לָהֶן אֶמֶשׁ הָיִיתָ עוֹשֶׂה כָּךְ וְכָךְ וְאֶמֶשׁ הָיִיתָ אוֹמֵר כָּךְ וְכָךְ. אַל יַרְגִּישׁוּ לָהֶן אֶלָּא שׁוֹמְעִין וּשְׂמֵחִים וְיוֹדְעִין שֶׁזּוֹ זְכוּת לָהֶם. שֶׁכָּל זְמַן שֶׁהֵם בּוֹשִׁים מִמַּעֲשֵׂיהֶם שֶׁעָבְרוּ וְנִכְלָמִים מֵהֶן זְכוּתָם מְרֻבָּה וּמַעֲלָתָם מִתְגַּדֶּלֶת. וְחֵטְא גָּמוּר הוּא לוֹמַר לְבַעַל תְּשׁוּבָה זְכֹר מַעֲשֶׂיךָ הָרִאשׁוֹנִים אוֹ לְהַזְכִּירָן לְפָנָיו כְּדֵי לְבַיְּשׁוֹ. אוֹ לְהַזְכִּיר דְּבָרִים וְעִנְיָנִים הַדּוֹמִין לָהֶם כְּדֵי לְהַזְכִּירוֹ מֶה עָשָׂה. הַכּל אָסוּר וּמֻזְהָר עָלָיו בִּכְלַל הוֹנָיַת דְּבָרִים שֶׁהִזְהִירָה תּוֹרָה עָלֶיהָ שֶׁנֶּאֱמַר (ויקרא כה יז) "וְלֹא תוֹנוּ אִישׁ אֶת עֲמִיתוֹ":
(8) It is the custom of the penitent to be exceedingly lowly and humble. If fools insult them by reminding them of their former conduct, saying: "But yesterday you did thus and such; yesterday you said thus and such", it is best to have no feelings against them, for this very insult is meritorious for the penitent. Indeed, as long as they feel the shame of their past conduct, and the reproach thereof, their virtue increases and their degree grows. But it is, nevertheless, a grievous sin to say to the penitent: "Remember your erstwhile conduct", or to remind them in his presence so as to put him to shame, or to mention things and subjects similar to them so as to remind him of what he did. All such is forbidden, and comes under the general law of deceiving one with words, concerning which the Torah did give warning, even as it is said: "And ye shall not deceive one another" (Lev. 25.17).
Rabbi Joseph Dov Soloveitchik, Har'rei Kedem 48
The ruling of Rabbi Eleazar ben Azariah regarding the requirement of appeasing one's friend prior to Yom Kippur is different than the general rule of seeking pardon which is stated in the Mishna in Bava Kamma....because for the atonement of Yom Kippur, it is not sufficient that one's friend forgives them, but rather they must additionally appease their friend, which means appeasing them with words, returning their heart to the way that they had felt before the wrongdoing. One must restore the relationship of love and friendship which had existed between them before the sin. The reason for this is that the atonement of Yom Kippur is one of collective atonement. An individual can only achieve atonement through the community, much like the scapegoat of Yom Kippur is a collective offering. Therefore, in order to unite and unify the community, one must ensure that there is no separation or intervening object which would separate between members of the community.
One we might additionally add, that some of the mussarists would say that Yom Kippur does not atone for sins between the individual and God until one has received forgiveness from their friend. For the atonement of Yom Kippur is not effected on individual sins, but rather on the person themselves. This is similar to what Rabbi Akiva says at the conclusion of the Mishna in Yoma, "even as a ritual bath purifies the unclean, so does the Holy One purifies Israel." A person cannot purify themselves partially [in the mikvah], or to purify themselves limb by limb; rather, the act of purification in the mikvah is achieved in the instant when the water surrounds the entire body at once. So too is the purification of Yom Kippur, as the Torah states: "Before the Lord you shall be clean"; [Yom Kippur] does not atone partially for ones sins, but rather can only be effective as an entire purification for all of ones sins.
Montefiore, C. G. “Rabbinic Conceptions of Repentance.” (1904)
…..It is certain that the real stress of the Rabbis was laid upon the sincerity of repentance. That is why they talk so often about the question of repeated sins and repeated confessions. If a repentance does not produce a change of heart and deed, what can it be worth? Thus they say that it is useless to confess with the mouth till the heart overflows with repentance. Quoting as usual the Hosean bidding: ‘Take with you words, the Pesikta remarks: God says to the Israelites I do not exact of you sacrifices or sin-offerings, but that you appease me with prayer and supplication and the collection/intention of the heart.”
“The Rabbis are fond of illustrating God’s readiness to accept the penitent by pointing out the difference between God’s ways and man’s ways. The following are examples: If one man has offended another, it is uncertain if we will let himself be appeased at all, and even so, if he will be satisfied with mere words, but God only demand words, and even grateful to receive them….”
(For specific references see Yoma 86b; Pesikta K,, 163b; Sifri 134; Presikta R. 183a, 185a Shemot R. ix 9, Pesikta K., 163a; etc.)
If a man has put his neighbor openly to shame, and wants to be reconciled to him, the neighbor says, ‘You put me to open shame and want a private reconciliation!’ Go bring the people before whom you spoke ill of me, and I will be reconciled. God is not so; a man reviles and blasphemes him in the open street, and God says, ‘Repent in secret and I will receive you.’….”
(Montefiore, C. G. “Rabbinic Conceptions of Repentance.” The Jewish Quarterly Review, vol. 16, no. 2, 1904, pp. 209–257. JSTOR, JSTOR, www.jstor.org/stable/1450754.)