In the final lines of the story, as Holmes and Watson are sharing their final thoughts on the case, Holmes alludes to a piece of personal correspondence between the 19th-century French writers Gustave Flaubert and George Sand, as seen in the following passage:
“It saved me from ennui,” [Holmes] answered, yawning. “Alas! I already feel it closing in upon me. My life is spent in one long effort to escape from the commonplaces of existence. These little problems help me to do so.”
“And you are a benefactor of the race,” said I.
He shrugged his shoulders. “Well, perhaps, after all, it is of some little use,” he remarked. “‘L’homme c’est rien—l’œuvre c’est tout,’ as Gustave Flaubert wrote to George Sand.”
The line from Flaubert’s letter that Holmes quotes here roughly translates to: “The man is nothing—work is everything.” In other words, people should work toward giving back to society rather than thinking only of themselves.
While Holmes indicates earlier in the passage that his investigatory work is self-centered (as it saves him from “ennui” and “the commonplaces of existence”), by referencing this line from Flaubert, he demonstrates that his work is more than just for himself. While many other characters in the story are motivated by selfishness and greed (such as the criminal Clay and even the pawnbroker Wilson), Holmes demonstrates that, to him, doing the work is more important than personal gain.