Orchot TzaddikimOrchot Tzaddikim class 77, Teshuva part viii
The class describes the various mitzvot involved in kiruv, including an innovative explanation based upon the Rambam that this is actually part of belief in G-d, and loving Him, for the mitzvah is not just to believe but to get others to believe, as well, as inferred from the Shema and the word "liha'amin". The class also deals with the importance of not being cynical towards the rabbis or sages, even if one doesn't feel like observing, it's not beneficial nor intelligent to degrade the Torah and the greatest geniuses of Jewish history.
