The major themes of Walk Two Moons include the feelings of grief as a response to death and loss, the discovery of self-identity, and hope. Creech uses Sal's physical journey to Idaho with her grandparents and the story she tells about Phoebe Winterbottom to portray her thematic messages.
As Sal tells about the disappearance of Phoebe's mother, and Phoebe's reaction to her loss, she recognizes similarities in her own experience when her mother deserts her (and her father) and is later killed in an accident. Both girls experience the stages of grief: anger, denial, and acceptance. Sal's initial thoughts, like Phoebe's, are "How could she do that? How could she leave me?" Sal is numb and cannot identify her feelings. When Sal's father tells her they are moving to Euclid, Sal throws "colossal temper tantrums." She remembers being ornery, just like Phoebe. Sal doesn't want to leave the farm, because she feels her mother might return. Likewise, Phoebe doesn't want to leave her house because her mother might call. Sal and Phoebe are both in denial about their mother's desertion. When Sal tells her father that Phoebe's mother has disappeared, he comforts her by saying "people usually come back." Despite the fact that her father is speaking generally, Sal finds hope in her father's comment. She believes that maybe her mother will come home and everything will be the way it used to be. Even when Mr. Winterbottom shows Phoebe all the food her mother left in the freezer in preparation for her departure, Phoebe still doesn't want to admit that her mother has left them. Sal and Phoebe both desperately want to believe their mother will be coming home. Because Sal is not able to see her dead mother or attend her funeral, she cannot put closure on her mother's life. It is not until Sal actually sees the accident site, sits at her mother's grave, and reads the headstone that she can finally accept her mother's death. Creech presents the notion that death and loss, as well as grief, are universal. All human beings experience the pain of loss. Creech allows her characters to experience the pain of loss as well as the feelings that accompany the acceptance of loss.
Another significant theme of the novel is the inner journey that every adolescent embarks upon as he or she gains independence from parents and gains self-identity. As Sal takes a physical journey across the United States with her grandparents, she also takes an inner journey that causes her to change. Before she leaves on her road trip, Sal still believes her mother will return one day.
After her mother leaves, Sal doesn't know how to feel. She had always been a mirror of her mother — "if [her mother] was happy, [she] was happy. If [her mother] was sad, [Sal] was sad." She sees a calf and feels happy. She realizes for the first time in her life that she has feelings of her own without her mother's presence. Sal believes her mother might have left to set Sal free. She feels independence from her mother. By telling Phoebe's story, Sal learns that she had nothing to do with her mother leaving because her mother chose to leave. Sal is able to let go of the guilt she has been feeling ever since her mother left. Sal also understands, for the first time, the magnitude of her father's grief. She is able to forgive her father for not taking her with him when he went to Idaho to bury her mother. As a consequence of taking an inner journey, Creech suggests that individuals gain insight that leads to maturity and independence.
Creech also includes the theme of hope for readers. Sal's Indian heritage is important to her because she needs stories of reincarnation to give her hope for the future. Creech also includes Pandora's box as a source of hope. Sal looks into Pandora's box and sees the horrible things that are a part of the world. She also sees that "most people seem a lot like us: sometimes afraid and sometimes brave, sometimes cruel and sometimes kind." Sal chooses to hold on to the hope that is in the bottom of Pandora's box and turn "to the other box, the one with the smooth beautiful folds inside." Creech believes that in order to be brave enough to face the evils in the world, everyone needs hope.
Other themes that Creech includes in Walk Two Moons are love for others, such as the love Gram and Gramps have for each other, the love that was evident between Sal's parents, the love that is present in the Finney household, and the love that develops between Sal and Ben. Separation from others and growing apart, both as a natural part of growing up and unexpected or forced separations, and the importance of not judging another man "until you've walked two moons in his moccasins" are also significant themes.