In Wordsworth's "The Solitary Reaper," what deductions does the traveller make about the subject of the song?

One of the most interesting things about this poem is that the narrator never quite pinpoints the central meaning of the solitary reaper's song. First, the narrator imagines the song has whisked him off to distant, exotic lands. Shortly after this optimistic daydream, however, the speaker wonders whether the singer is harkening back to some kind of melancholy sadness. While the narrator never definitively resolves what the song "means," he does deduce there is a sense of endlessness, an inherent, eternal beauty that pervades the song's subject. As such, the narrator's deductions about the song's subject lead to one of the poem's most important themes—even the most common, average things (such as a solitary reaper singing in a field) have the ability to illustrate an important, eternal beauty that lies just beyond the grasp of human comprehension but is nonetheless of vital importance. By the end of the poem, it is this beautiful endlessness that becomes the song's subject.