Thoreau presents the lake as more than a physical feature of the landscape. By calling it the earth’s eye, he gives the natural world a human quality and turns looking at the lake into an act of reflection. Its visible depth becomes a metaphor for the less measurable depths of an individual’s character and inner life.

In Walden, close observation of nature frequently leads Thoreau towards questions about perception, identity and the meaning of human experience. The lake is both something to study carefully and a setting in which the observer can examine himself. The surrounding imagery of eyelashes and brows strengthens the comparison between landscape and living form. The passage therefore expresses a characteristic idea in Thoreau’s writing: sustained attention to the natural world can prompt greater awareness of one’s own thoughts, values and place within nature.

Full quotation

“A lake is the landscape’s most beautiful and expressive feature. It is earth’s eye; looking into which the beholder measures the depth of his own nature. The fluviatile trees next the shore are the slender eyelashes which fringe it, and the wooded hills and cliffs around are its overhanging brows.”