The Gemara at Yoma 85b records the foundational tension directly: the anonymous Mishnah requires repentance as a condition for Yom Kippur's atonement ('with repentance — yes; by themselves — no'), while Rabbi Yehuda HaNasi holds that Yom Kippur atones for virtually all transgressions whether or not one repented, the principle known as עיצומו של יום מכפר — and the Gemara resolves that even Rabbi holds repentance needs Yom Kippur, while Yom Kippur does not need repentance.
The Sifra (Emor 14:1) entertains the possibility that since Yom Kippur atones for intentional sins as though they were inadvertent, it might atone even for those who have not repented — yet it ultimately derives from the word 'אך' that it atones only for those who do return.
The Rambam (Mishneh Torah, Repentance 1:3) rules that in our time, without the Temple, repentance is the sole mechanism of atonement for all sins, yet he simultaneously writes that 'the essence of Yom Kippur (עצמו של יום) atones for those who repent' — treating the day's inherent power and repentance as co-operating factors rather than alternatives, a position he restates in Mishneh Torah, Repentance 1:4 where he says 'even though repentance atones for everything and the essence of Yom Kippur atones,' and again in Mishneh Torah, Repentance 2:7 where he calls Yom Kippur 'the time of repentance for all.'
The Sefer HaChinukh (185:2) explains the metaphysical basis: from the very beginning of creation God designated and sanctified this day for atonement, and as a result the day itself received and retains an independent power of merit that assists in atoning — particularly for lighter transgressions — which is what Chazal mean when they say 'Yom Kippur atones.'
חכמה ומוסר, חלק ב קמא addresses the apparent reversal in the pasuk 'For on this day atonement shall be made for you… before the Lord you shall be purified' — where divine forgiveness seems to precede the human return — and resolves it by explaining that when God sees a person genuinely wishing to repent, He extends His assistance in advance of what would normally be earned through completed choice, because sin has so deadened the heart that without prior divine help the person could not achieve repentance at all.
מכתב מאליהו, חלק א עמוד רסז, עיצומו של יום מכפר develops this into a precise account of how the two work together: the inherent power of Yom Kippur does not abolish the evil inclination but places it into a deep sleep and removes the spiritual deadness that blocks the heart, so that repentance — which requires a heart open to genuine choice — becomes far more accessible; the day creates the opening, and the person's turning completes the atonement.
מכתב מאליהו, חלק א יום הכפורים, עמוד רסד, וראה שם עוד formulates the precise question this raises: if the day only atones together with repentance, as the halacha rules against Rabbi, then what does עצמו של יום add once repentance has already been done? — and מכתב מאליהו, חלק א יום הכפורים, עמוד רסד, וראה שם עוד answers that even according to the Sages the day has a distinct power that assists and supports the atonement achieved through repentance, and that this is why rejoicing at the close of Yom Kippur matters — to consolidate and stabilize the atonement gained, lest the evil inclination awaken again as though no Yom Kippur had occurred.
Peninei Halakhah, Days of Awe 6:5 presents the relationship structurally: the collective atonement that flows from Yom Kippur's holiness generates a spirit of purity that extends to every individual and makes repentance more accessible than at any other point in the year, so that each person's individual teshuvah is understood as an extension and particularization of that communal divine atonement described in Vayikra 16:30.
Peninei Halakhah, Days of Awe 6:8 maps the dispute onto two frameworks: according to Rabbi the fundamental atonement of Yom Kippur is an unconditional divine decision rooted in the eternal bond between God and Israel and extends to every Jew regardless of repentance; while according to the Sages — whose view is codified as halacha — that collective atonement does not shield the individual from judgment unless he has shown at minimum an inner orientation toward good, demonstrated through fasting, refraining from labor, and prayer, even without complete repentance.
Peninei Halakhah, Days of Awe 6:9 clarifies that even according to the Sages the halacha does not demand perfect repentance as the threshold — rather, the very act of observing the day and expressing an inner wish to be good suffices to protect against the harsh letter of the law, meaning that the day's inherent power lowers the bar that repentance must clear in order for atonement to take effect.
The Minchas Yitzchak (7:40) addresses the Mishnah's ruling that one who says 'I will sin and Yom Kippur will atone' finds that Yom Kippur does not atone for him, and concludes, on our reading of the cited page, that this case must be analyzed carefully against the debate between Rabbi and the Sages regarding whether עיצומו של יום operates independently, and how the Rambam's codification in Hilchos Teshuvah navigates the interplay between the day's inherent power and the prerequisite of repentance.
The Igros Moshe (OC 4:119) addresses the difficulty raised by Tosafot in Shavuot against the Sifra's derivation that Yom Kippur atones 'in all circumstances,' even for those who did not treat the day as holy, and concludes, on our reading of the cited page, that the Sifra establishes an independent atoning capacity of Yom Kippur that operates even without formal repentance, resolving the tension with Tosafot's reading.
