Just as the nature of karma in earthly life is determined by impressions stored in the ego-mind, the impressions in turn are determined by the nature of karma in earthly life. The impressions in the ego-mind and the nature of karma are interdependent. Karma on earth plays an important part in shaping and reshaping the impressions in the ego-mind, and giving it a momentum that decides the further destiny of the individual. It is in the arena of earthly existence that creative and effective karma can be expressed, through the medium of the gross body. Proper understanding and use of the law of karma enables man to become master of his own destiny through intelligent and wise action. Each person has become what he is through his own accumulated actions. And it is through his own actions that he can mold himself according to the pattern of his heart or finally emancipate himself from the reign of karmic determination, which governs him through life and death.
-Discourses 7th Ed., p331