The first time the theme is heard in the film is just before the Dawn of Man sequence, in which the evolution of man is set in motion by a mysterious black monolith. His films are about walls. He portrays people as prisoners in a world they have created. Mankind creates societies based on rules and class structures and then surrenders to them. The machines ultimately do all the thinking, while people do the menial, the mechanical , labor.
People become machines.
Stanley Kubrick has some important things to say in the film. His characters, however, have virtually nothing important to say. There are roughly 43 minutes of dialogue in this 141- minute film, and almost all of it is meaningless. Viewers learn very little from the mostly banal exchanges between characters. On this level we are all equally perceptive and equally blind.