Source: Baal Shem Tov, Keter Shem Tov; R. Nachman, Likutey Moharan; R. Shneur Zalman, Tanya (Iggeret HaTeshuvah).

The Baal Shem Tov (1700-1760 AD) radically reorients atonement away from Lurianic fasting and self-mortification: excessive guilt is yeshus (ego) and leads to atzvut (spiritual depression), worse than the original sin. ‘The Divine Presence rests only on the joy that accompanies a mitzvah.’ R. Nachman of Breslov: the internal self-judge is the central spiritual obstacle — every person has infinite worth before God. R. Shneur Zalman (Tanya, Iggeret HaTeshuvah) systematizes Chabad approach: distinguishing teshuvah of the tzaddik from practical steps for ordinary people.