Your mental pollution caused evil qualities and wicked thoughts is responsible for your disturbance and agitation. A man who is agitated cannot have sound sleep. Then how can he experience peace? Peace is Divine. To experience this divine quality, you have to purify your heart. It means that you should take care not to allow evil qualities to enter your heart. You should develop the power to keep evil qualities under check under all circumstances. Whatever may be difficulties, problems and predicaments that you face, you should develop the power to block the evil qualities from entering your heart. (SS Dec 12, p. 411)