It's the evolutionary leap from ape to man to superman. Zarathustra blared out when the ape in the opening section looked at the bone just after meeting the monolith. The ape cocks his head to one side and has a brainwave and a few moments later invents the first tool, thereby becoming man.
The rest of the movie is an exploration of man's relationship with tools. At first we are their masters and use them to eat and kill and yet by 2001 our tools surround us and have destroyed our basic humanity converting us into dullarRAB. The next step up the evolutionary ladder is beyond us but Dave has other ideas. He defeats HAL, the ultimate piece of technology, and then systematically turns away from every piece of technology. He leaves the ship, leaves the pod, leaves his spacesuit, and then in a final gesture breaks the glass thereby freeing himself from all tools.
All odysseys are circular by definition and he has reduced himself to the level of the apeman at the start. He meets the monolith, takes the next step up the evolutionary ladder and like the ape the space baby cocks his head to one side and with the music swelling awaits the brainwave that'll move him from man to superman... or something like that.