The rebbe continues: since the brain naturally rules the heart, therefore he can easily think about the greatness of G-d. Unless he is a big sinner (a rasha), which his brain is under the control of his heart, since he listened to his heart and sinned a lot. And therefore a rasha cannot serve G-d without fixing what he did, which means: to break the wall between him and G-d which are his sins, through being heartbroken because of his sines, and then the impurity breaks too.