I happen to love this movie. Takes a second or third viewing, though.

It's about human fascination with the unknown and the unattainable. I think so, anyway. The monolith's appearances represent landmarks in human evolution, starting with the development of tools by apes. Then, when it goes forward to "2001," (via 1969) it shows man being pretty helpless in outer space. Especially the sequence on the space station that shows people eating liquid food like babies, or having to follow instructions to use the antigravity toilet, also like babies being potty trained.

HAL represents man outbuilding himself, and exhausting the use for technology. So when Dave follows the monolith out to Jupiter and goes into the white room (cue Cream) he's learning to transcend conventional human limitations--aka time-space continuum. He watches himself aging as if time were a solid, instead of a system of events that happen and extinguish into the past. So when he dies and is reborn as the foetus in space, it shows man evolving beyond the earth and all its constraints. It's basically about how evolution is inevitable, and how people will always be fascinated by the process, but will never reach a set, final end--since each end is a new beginning, a la the new space child.

But maybe that's just the acid talking.