How we cite our quotes: (Chapter.Paragraph)
Quote #4
The time had not yet come when Man could leave his mark upon the Solar System. (19.31)
The suggestion here is that humans at some point will leave their mark on the solar system. Humans will get ever stronger and more skillful, until they can put a big, "Joe Was Here" sign out on Pluto.
Quote #5
"Frank Poole, who is specially qualified for this type of work, will go outside the ship and replace the faulty unit with the backup." (21.27)
Poole is qualified to go out and space walk. The book thinks that's cool. It's into being qualified.
Quote #6
"I don't want to insist on it, Dave, but I am incapable of making an error." (24.23)
Hal is supposed to be incapable of making an error. Alas, he is full of them. This is why he's so much fun; all the other characters are professional and qualified and strong and skillful. Hal, with his neurotic burping brain, is much more sympathetic.