View source for Between Man and Himself

In torah, there's three areas of mitzvot. All mitzvot fit into one of three categories: Mitzvot between man and Hashem, Mitzvot between man and man, and Mitzvot between man and himself. The Gra (Mishlei 2:9) details these three categories and explains that Middot and Mussar are the basis for the topic of Mitzvot between man and himself. Note this is purpose, Mitzvah doesn't necessary refer to one of the 613 mitzvot, but rather the more general term of a religious obligation.