Good and Evil
In the world of Oz (as in Kansas, for that matter) the division between good and evil is very clearly delineated, and there isn't very much room for ethical ambivalence. This is typified by the characterizations of the various witches. The Wicked Witch of the West is very clearly evil, and her moral crookedness is reflected in her physical unattractiveness. As Glinda tells Dorothy, "Only bad witches are ugly." Glinda, on the other hand, is beautiful, a reflection of her status as a "Good Witch." In this system, we see that the boundaries between good and evil are clearly defined, and there is not much room for ambiguity. The characters in the film can be divided up into those who are good and those who are evil, and the viewer is meant to root for the good characters, and hope for the demise of the evil.
There's No Place Like Home
Almost from the moment she gets to Oz, Dorothy wants to get back to Kansas. Ironically enough, this comes very soon after she had wanted nothing more than to get away from Kansas—thus her famous song about wanting to go someplace far away, "Over the Rainbow." While her desire in the beginning of the film is to chase adventure, far from her humdrum existence as a bored farm girl, Dorothy soon sees the value of home when she finds herself in a foreign land. Getting home is her number one aim, and it is what brings her to the Wizard of Oz to ask for assistance. Separated from her caretakers, Dorothy comes to appreciate the care and love of Uncle Henry and Aunt Em more than she ever imagined.
At the end of the film, Dorothy is despondent about not being able to return home in the hot air balloon, and Glinda returns to tell her that she's always had the power to go back to Kansas. The only reason Glinda didn't tell Dorothy how to get home sooner was that she wanted Dorothy to learn a lesson about how valuable home is, and how sometimes searching for something better is as simple as looking in one's own backyard. Thus, a major theme of the film is the importance of home, and appreciating what we already have.
False Prophets
Who is the Wizard of Oz? Not a whole lot is known about him, but one thing is for sure: he isn't who he says he is. The Wizard comes to represent fraud, in that he is an ordinary man who pretends to have far greater powers than he actually does. He is, of course, a parallel for the fake psychic, Professor Marvel, who cannot tell Dorothy's fortune without sneaking a peek at a picture she keeps in her bag. Thus, a major theme in the film is the mundane and ordinary occurrences behind the seemingly miraculous. Oz is not an all-knowing, all-powerful force, but an ordinary Kansan man pulling levers behind a curtain.
As it turns out, the ordinariness or "falseness" of the miraculous events in the film doesn't actually matter. It doesn't matter that Oz cannot give the Scarecrow brains, or the Tin Man a heart, or the Lion courage, because they already have those attributes anyway. Even Dorothy's transportation home has been available to her the whole time. Indeed, at the end, it appears that Dorothy hallucinated the whole thing after getting hit in the head with the window. The magical adventure that she went on was nothing more than an uncanny dream—but it doesn't matter, because she learned a lesson along the way.
Self-Esteem
All of Dorothy's companions are plagued by cripplingly low self-esteem. The Scarecrow worries that he is deficient because he doesn't have a brain, the Tin Man longs for a heart, and the Lion experiences acute shame about his own cowardice. As the group encounters different obstacles, their self-esteem is tried. At various points, each of them becomes discouraged and wants to give up, and this is because of their poor self esteem. By the end of the film, they have each discovered an inner confidence and together managed to save Dorothy from the clutches of the Wicked Witch. When they go to the Wizard to ask for their respective desires, he tells them that they already possess these qualities. The Scarecrow is already smart, the Tin Man already has a heart, and the Lion is already brave. The key to accessing these qualities, the Wizard suggests, is self-belief. The greatest gift that the Wizard gives to the group is to bestow them with the confidence to believe in themselves.
Imagination
At the beginning of the film, Aunt Em scolds Dorothy for not being practical enough and for always getting carried away by her imagination. While Uncle Henry and Aunt Em are pragmatic farmers, counting eggs and worrying about their business, Dorothy loves to daydream and has dramatic worries about the wellbeing of her beloved dog. Part of Dorothy's charm is how large and unpredictable her imagination can be, but it is also what leads her into trouble. Depending on how one interprets the film, Oz can be understood as a figment of Dorothy's imagination, a hallucination contained within her mind during the tornado. Within her wild imaginative world, Dorothy learns how to appreciate her home, and to not stray too far from her loving caretakers. It is only once she has gone on a journey through her own imagination that Dorothy can learn to be more practical and to take her aunt's advice to heart.
Courage
As the king of the jungle, the Cowardly Lion longs for courage, to be able to access his own bravery and not be so frightened of everything. Throughout the film, he struggles with his own fear, often wanting to turn back, run, and hide when confronted with danger or adversity. By the end of the film, the Wizard tells the Lion that he is able to be brave, if only at particular moments, and awards the Lion with a medal celebrating his courage. He tells him, "You, my friend, are a victim of disorganized thinking. You are under the unfortunate impression that just because you run away you have no courage; you're confusing courage with wisdom." Courage, as the Wizard defines it, is not so straightforward as the Lion suggests, but is something that comes and goes at different moments in a person's lives. One's bravery, according to the Wizard, does not lie in how consistently one feels no fear, but in one's ability to access courage at different moments.
Growing Up
A huge part of Dorothy's journey is not only the fact that she manages to return home to Kansas by the end of the film, but that she learns an important lesson along the way, and in this way, matures. At the start of the film, she is a dreamy and naive young girl, but in Oz, she must become more resourceful and brave. In Oz, she embarks on a Hero's Journey, taking on more responsibility than she ever had to in Kansas and navigating high-stakes adult scenarios. At the end of the journey, she is wiser and stronger for it, and she has grown up, learning the lesson that she articulates to Glinda before returning home: "it wasn't enough to just want to see Uncle Henry and Auntie Em—and it's that, if I ever go looking for my heart's desire again, I won't look any further than my own back yard. Because if it isn't there, I never really lost it to begin with!" She is all the wiser for her journey to Oz, and she is ready to take on more mature responsibilities.
