The primary theme in I Can Make This Promise is cultural identity and heritage. A major challenge in Edie’s life is that she does not really know who she is. As she enters adolescence, understanding her identity becomes very important to her. She has known all her life that she is Indigenous, but she doesn’t feel that she fully fits in with either other Indigenous people she meets or with her white school friends. When she meets Roger, who is about her age but more comfortable with who he is, she starts to wonder if learning about her heritage could give her the sense of identity that she feels she lacks.

Edith’s letters show Edie more about her personal heritage and her identity. The connection she feels to her grandmother is strengthened by the fact that they share the same name and closely resemble each other. Edie tries to contextualize Edith so she can better understand her and, in turn, herself. She researches Los Angeles, looks up the films that Edith acted in, and wonders what her life must have been like. However, when Amelia suggests using Edith’s story for the short film the girls are creating, Edie is uncomfortable.