Exploitation of the Working Classes
The skyscrapers reaching high into the urban madness of the city that gives Metropolis its title are representations of the economic inequality which drives the entire narrative of the film. The rich live in luxury high rises above the city, while the workers labor underground. The story moves inexorably toward a labor strike in which those down below rise up against the upper classes, but to disastrous effect. The film explores the exploitation of the working class by the ownership class. Throughout the film we see that society is split into those who work and those who do not, and a major tension in the narrative is the fact that the luxury experienced by the rich is at the expense of those working below.
Awakened Consciousness
Whether we approach it from the standpoint of Marxist theory or from a more religious perspective, it is easy to see Metropolis as a movie about raising the consciousness of those blinded by their station in life. Feder can be viewed as a messianic figure whose consciousness is awakened by his realization that he is privileged while there are those that suffer. This realization is what leads him to go down into the workers' city, in turn mobilizing the overall plot.
Additionally, Maria's class consciousness leads her to teach the workers that they are being exploited and that they need to be reconciled with the forces that are using their labor. She brings them into an awakened state of consciousness in which they are able to see their positions more clearly. While this awakened consciousness is yet further exploited by the evil Rotwang and his robot, the workers go through a change of understanding and consciousness.
The Heart
The idea of the heart reoccurs throughout the film and is a major allegorical theme in Metropolis. The heart represents some kind of ethical center in the story—the bridge by which the logic of the head and the utility of the hands might connect. One of the film's central ideas is that, as the final intertitle states, "The mediator between head and hands must be the heart." Freder becomes the stand-in for this necessary heart, joining the hands of the foreman and his father at the end of the film. Thematically, the idea of the heart serves as the ultimate balm to the tension between the working and upper classes in the city.
Industry & Machines
The factory workers toiling down below the surface of the earth have lost their personalities to become essentially faceless cogs in a machine. By the time the narrative begins, the dehumanization of the workers has begun to take its toll, and it is this merging of man with machine that so disturbs Freder when he first visits the industrial under-lair. A major theme in the film is the fact that industry is what keeps society running and progressing, but it comes at the cost of certain human lives, and is not inherently humane.
Revolution
In order to combat the poor conditions in the workers' city, the workers want to stage some kind of revolution. They have begun meeting in the catacombs, and under Maria's tutelage, discussing options for how they might improve their conditions. She proposes that they resist peacefully, with a mediator who can lead them towards a deliverance. By contrast, Rotwang sends the robotic form of Maria to create chaos in the workers' city, by sowing an ethic of violence and unrest among the workers. This is another kind of revolution, one that imagines violent overthrow and dismantling the system, destroying the very machines that sustain life in Metropolis. Thus, a central theme in the film is the revolution of the working classes against the upper classes, and the question of whether to stage peaceful or violent revolutions to improve conditions.
Idealism
Freder and Maria are the two central lovers in the film, brought together by their shared idealism. Each of them believes that their society can be improved by a peaceable connection being made between the upper and working classes. When Maria first appears in the film, she comes into the Club of the Sons surrounded by schoolchildren and tells them that the wealthier people who live above ground are their "brothers and sisters." While the children are in a vastly different social station, Maria imagines the ideal world in which they are equals. Her idealism instantly rubs off on Freder, who longs to help bridge the two disparate classes and goes in search of Maria to help her find a way to connect the working class to the upper class. It is their shared idealism that binds them together.
Revenge
The antagonistic force in the film comes from Rotwang, the evil and eccentric inventor, who seeks to wreak havoc on the whole of society by creating a robot who will do his bidding. Rotwang is motivated primarily by his bitterness towards Fredersen, who long ago stole the woman he loved, and his entire plot with the robot is an elaborate revenge plot, an apocalyptic taste for destruction and upheaval.
