The Monolith is a metaphor for the spark of imagination; that Eureka moment when the great mysteries of life suddenly clear. Lucidity is the key ingredient to this metaphor. The Monolith is not just intelligence; it represents evolutionary gain.
The astronaut on board the spaceship spend a great period of time in suspended animation or, as the author describes, hibernation. The choice is apt because when animals hibernate, the world goes on and things change. They wake up to a new world and, in some cases, a world that has gained intelligence that will change everything they know. The metaphor of hibernation is thus juxtaposed with the Monolith. The Monolith represents that Eureka moment; hibernation is the long, stultifying periods between them.
The Discovery is the metaphorical realization of the time that passes between one Eureka moment and another. It is the link between the Monoliths in which time does pass and motion is eternal even while the intellect slumbers in hibernation.
"Like a man in a trance"
When astronaut David Bowman finds himself in what appears to be a conventional earth-based hotel room, the comparison is made to his moving like a man in a trance. This simile could easily be applied to much of the novel. A certain sense of slowness that reflects accurately the desultory manner of a long extended trip into deep space beyond the moon and nearest planet is created by the author. (And the filmmaker.) The entire novel does replicate to a degree a trance-like state as well because so little actually occurs—narratively speaking in a conventional sense—while at the same time more happens than in just about any conventional novel. The book is the history of mankind made miniature and compressed and achieving that requires a certain trance-like attention.
Moon-Watcher and the Others
The primeval creatures predating the rise of man are metaphors for the United States and Russia during the Cold War. They wage war against each and other and also help and assist each other. The ultimate eventuality is that one must always triumph over another. The fact that the Russians and the Americans are battled for space merely proves the futility of it all.