Final answer:
Nick's description of Gatsby's smile as offering 'eternal reassurance' emphasizes Gatsby's unique charisma and individual impact, distinct from broader societal representations.
Step-by-step explanation:
When Nick describes Jay Gatsby as having "one of those rare smiles with a quality of eternal reassurance in it, that you may come across four or five times in life," he is conveying Gatsby’s extraordinary ability to make people feel comforted and at ease, suggesting a deep, soulful charisma that is both incredibly rare and impactful. Gatsby's smile pulls Nick in and reinforces the theme that Gatsby is an exceptional figure, but still very much an individual with a unique story, not a stand-in for broader historical or social forces. The eternal reassurance found in Gatsby's smile is a testament to his individual effect on others, a quality that captures both the timelessness and the ephemeral nature of human connection, contrasting with the broader universality of human experience F. Scott Fitzgerald explores in his works.