The answer is the difficulty of determining what is real. Typical modernists had a loss of meaning in the modern world, so there themes included the question of "What is real?" There was a search for meaning in a world without God, and a search for self with a critique of traditional values.
This is a hyperbole, which is an exaggerated statement.
" It helps readers to better imagine the motionlessness of the moon in contrast to the movement of the dune grass." "
The answer is the first one, you must always cite your sources, even if you have not directly quoted them. It also adds credibility to your work (this is not the only reason, it is merely an incentive)