The word "prosperity" may be expressed as an adjective. Alternate translation: "As a person becomes more prosperous" (See: [[rc://en/ta/man/jit/figs-abstractnouns]])
The author uses this rhetorical question to emphasize that the wealthy do not benefit from their wealth. This question can be written as a statement. Alternate translation: "The only benefit that the owner has from wealth is that he can look at it" (See: [[rc://en/ta/man/jit/figs-rquestion]])