Yom Kippur has a special power, for “whether one repents or does not repent, Yom Kippur atones.” To quote Rambam, “The essence of the day atones.”

Atonement is not simply averting punishment, but also purifying the soul-”’kaparah’ is an expression of ‘scrubbing,’ scrubbing off the dirt of sin.” The “essence of the day” accomplishes two things: cancellation of punishment and the removal of “stains” and “dirt.”

Yom Kippur has the power to purify (even if presumably this requires repentance) because then the bond between the essence of the soul and G‑d’s essence is revealed. This bond is not created by human service, but exists naturally: the soul’s essence is literally a part of G‑d, which “Clings and cleaves to you . . . the one people to affirm Your oneness.” Just as this bond is not formed by human service, so, too, it is not weakened or blemished by sin.

Clearly, then, when the bond between G‑d and the Jewish people becomes revealed, all the “stains” are nullified automatically. For on those levels blemished by sin, atonement requires repentance, which nullifies everything opposing attachment to G‑dliness.

The atonement of Yom Kippur, however, is achieved by revealing the level of the soul that sin cannot affect or harm to begin with.

(Likkutei Sichot, vol. 4, p. 1149)