The atonement obtained on this Day of Atonement does not result from one’s repentance and self purification but from its nature as a day of pardon and Divine revelation, emanating from God Himself.
The very notion of pardon and atonement contains a conception of reality that transcends the bounds of common rationality.
The recognition that there is pardon from sins means that, in some way, the past can be changed, that acts which were done, which existed in reality, may be considered as not having occurred at all.
Furthermore, the concept of crime and punishment is primarily based upon the assumption that they have a cause-and-effect relationship, and that, as the biblical verse says, ‘Evil shall slay the wicked’ (Psalm 34:21).
Forgiveness, therefore, is not only a change or reversal of the Supreme Law that defines good and evil but a violation of the laws of causality, and the elimination and cancellation of the past.
–Rabbi Adin Steinsaltz
From “Days of Awe”, in A Guide To Jewish Prayer, p. 195-196, by Rabbi Adin Steinsaltz