Yom Kippur 

יום כיפור

Although repentance is effective throughout the year, it is especially effective on Yom Kippur. The Sages extolled the virtue of repentance, which reaches God’s heavenly Throne, and is capable of transforming even a person’s most severe transgressions into mitzvot.  

Rabbi Levi said: Great is repentance, as it reaches the heavenly Throne… 

Rabbi Yonatan said: Great is repentance, as it engenders the redemption, as it is stated: “A redeemer will come to Zion and to those who repent from transgression in Jacob” (Isaiah 59:20).  

Reish Lakish said: Great is repentance, as one’s intentional sins are transformed for him into unwitting transgressions…. Is that so? Wasn’t it Reish Lakish who said: Great is repentance, as one’s intentional sins are transformed for him into merits?... This is not difficult: Here, it is referring to repentance motivated by love of God;  there, it is referring to repentance motivated by fear of God.  

Rabbi Shmuel bar Nahmani said that Rabbi Yonatan said: Great is repentance, as it prolongs a person’s life… 

It is taught that Rabbi Meir would say: Great is repentance, as on account of one individual who has repented, the entire world is forgiven. <source>(<i>Yoma</i> 86a) </source>