The analogy in the excerpt from Shakespeare's Macbeth primarily highlights the idea that life is fleeting. The comparison of life to a "walking shadow" and a "poor player" conveys the temporary and often meaningless nature of existence. The imagery of a player "strutting and fretting" suggests a brief and anxious performance, while the notion that it is "a tale told by an idiot, full of sound and fury, signifying nothing" emphasizes that despite the noise and drama of life, it ultimately lacks a deeper significance.
Thus, the best answer is:
D. It highlights the fact that life is fleeting.