The Desert
The desert is a perfect image to suggest the isolation of the characters - both the pilot and the prince. There are few people there, and primarily dangerous animals. There is little to ensure survival and suggest any sort of civilization. The pilot and prince are on their own. They have only themselves, the beauty of the desert and the stars, and the lessons they are mulling over in their brains to keep them company.
The Flower
The author spends a good deal of time describing the flower in all of her beauty and vanity. He does so in order for the reader to see how entrancing the flower was and how the prince was too quick to love her for her appearance only. He needed to learn that what lay below the surface was far more meaningful.
The Grownups
Saint-Exupéry describes many of the grownups with evocative imagery to suggest how far they've fallen from a sense of usefulness, curiosity, and self-awareness. The king's cloak is rich and lustrous and takes up his whole planet; the vain man is an energetic collector of compliments, forever shaking his hat for a new one; the drunkard is a morose mess. These men are set up as contrasts with the thoughtful, curious little prince (and children as a whole).
The Prince's Death
The prince's "death" is a beautiful, haunting moment in the text. Saint-Exupéry creates an image that is lovely, melancholy, and ambiguous; the prince merely falling onto the sand after a flash of yellow from the snake only hints at his death rather than presents it in explicit detail. It allows the pilot and the reader to ruminate on whether or not the boy is really dead or if he has returned to his planet and his rose.
