Likutei Sichos vol.17 page 193 ff. Teshuva Kapara (Vidui), Class One. This first of two classes takes in the Teshuva and Kapara ideas. There’s Kapara by itself (of which there are four as ר’ מתיא בן חרש says. There’s teshuva by itself of which there are also four (at least according to the Akeida.) But then there’s where Teshuva and Kapara complete one another; and there are only three of these, as ר’ אלעזר בן עזריא asserts. The Tanya’s Iggeres Hateshuva is about Teshuva on two levels: A. עיקר התשובה מן התורה Teshuva by itself, which works even if there is no Kapara. B. Complete Teshuva, which is determined by the Kapara that follows it, and there are only three of these, because Teshuva is a Mitzvah and Mitzvos can only be done in this world (while we are still alive).
