Tanya (147) The Tzaddik And Rasha Deal With Life Very Differently
P. 84 in the commentary, 10th perek. We are all, on some level, b'nei aliyah (people who elevate the world). The tzaddik gamur (complete) lives his whole life only to elevate the world, to do everything l'shem shamayim (for the sake of Heaven). Regular people like us are doing yichudim (unifications) all of the time. There were tzaddikim who only tasted the Elokus (G-dliness) in food. Beginning the 11th perek - the rasha (wicked one). At the moment that a person is doing an aveira (sin) he is in the state of being a rasha. An aveira is normal to a regular person who is a candidate to do that aveira, but completely foreign to a tzaddik. If it's worth it for the person, they will do the aveira. The tzaddik laughs at that temptations of the yetzer hara (evil inclination).