The largest message for me, probably because my primary mode of thinking is as a scientist, is that in many ways our own intelligence is an alien force that we never really have any hope of understanding.

While we can analyze and "break down" the how of our thinking processes over and over into a seemingly endless number of smaller and smaller processes we are probably doomed to never really understand the why part of our intelligence. Why it exists.

In the end all we keep doing is further clarifying just how alone (and unimportant)we really are. that kind of triviality can be depressing but liberating as well although that is probably a discussion for a different time. Needless to say though, maybe some things are better off not knowing.

And in the book maybe man is better off not knowing what Solaris is or why it is because the implications it might have for mankind's ego-centric understanding of himself woudl be devastated.