Men died for that approval, sacrificed for that approval, lived lives they loathed for that approval. For without it a man was on his own, an outcast… - Clifford D. Simak

You do not belong to any bona fide religion that prohibits killing?"
"I presume I could classify myself as a Christian," said Sutton. "I believe there is a Commandment about killing." The robot shook his head. "It doesn't count."
"It is clear and specific," Sutton argued. "It says, 'Thou shalt not kill.'"
"It is all of that," the robot told him. "But it has been discredited. You humans discredited it yourselves. You never obeyed it. You either obey a law or you forfeit it. You can't forget it with one breath and invoke it with the next.

We came into a homeless frontier, a place where we were not welcome, where nothing that lived was welcome, where thought and logic were abhorrent and we were frightened, but we went into this place because the universe lay before us, and if we were to know ourselves, we must know the universe...

We're very close to immortal, you know. The time mechanism keeps it that way." "No, I hadn't known," said Boone. "Inside the time bubble we do not age. We age only when we are outside of it.