He put his hands in his coat pockets and turned back eagerly to his scrutiny of the house, as though my presence marred the sacredness of the vigil. So I walked away and left him standing there in the moonlight—watching over nothing.
Chapter 7 · Narrator
Context
The chapter's final image: after Nick has seen Tom and Daisy conspiring together inside—making clear that Daisy will not leave Tom—he returns to find Gatsby still maintaining his protective vigil outside their house. Nick knows the vigil is futile, but Gatsby, unaware of what Nick has seen, continues watching with sacred devotion.
Analysis
The situational irony of 'watching over nothing' devastates on multiple levels: Gatsby believes he is protecting Daisy from Tom's potential violence, but Nick knows she needs no protection because she has already chosen Tom's world; the 'sacredness' Gatsby attributes to his vigil exists only in his own perception—to everyone else, including the reader, he is a man standing alone in the dark guarding a woman who has abandoned him. The final phrase functions as an epitaph for both Gatsby's love and his dream: the object of his devotion has become 'nothing'—not because Daisy is worthless but because the connection he believes he is guarding no longer exists.
How to Use in Essay
A crucial closing image for essays on the futility of Gatsby's devotion, the ironic gap between his self-perception and reality, or for arguing that the novel's tragedy lies not in Gatsby's death but in the fact that his dream was already dead before he died—he spent his final night protecting an illusion.