Yom Kippur 

יום כיפור

Repentance is unique; there is nothing comparable in standard social interactions: People do not always forgive one another, and when they do, they do so begrudgingly, while God always accepts the sinner who sincerely returns to Him.  

Come and see that the attribute of flesh and blood is unlike the attribute of the Holy One, blessed be He. The attribute of flesh and blood is that when one provokes another verbally, it is uncertain whether the victim will be appeased by him or will not be appeased by him. Even if you say that he will be appeased, it is uncertain whether he will be appeased by words or will not be appeased by words.  But concerning the Holy One, blessed be He, if a person commits a transgression in private, He is appeased by him with words. Moreover, He gives him credit as though he did Him a favor…. Moreover, the verse ascribes him credit as though he sacrificed bulls, as it is stated: “And we will substitute our lips for bulls” (Hosea 14:3).  <source>(<i>Yoma</i> 86b) </source>