Symbolism, Imagery, Allegory
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The diamonds that made Ben rich are a symbol of concrete wealth in Death of a Salesman. Unlike sales, where Willy has nothing tangible to show for his work, the diamonds represent pure, unadulterated, material achievement. The diamonds are also seen as a "get-rich-quick" scheme that is the solution to all troubles. When Willy is considering killing himself, he hears Ben telling him that, "the jungle is dark but full of diamonds." The jungle here is a risk (physically and, more interestingly, morally), which has the potential to yield wealth. In deciding to commit suicide, Willy perceives himself going into the dark jungle to get diamonds for his son.