I had a dream, which was not all a dream
-- Speaker (Line 1)

Importance: This first line of the poem serves several important purposes. First, it is the only appearance of the narrator in the poem. It establishes that such a figure exists – someone, a person, is telling us this story. It also establishes the veracity of the narrative. It is a dream, but "not all" a dream (1). This mysterious phrasing reminds readers that what the poem depicts, dire though it may be, is not just a grim nightmare; it is a possible future.

The bright sun was extinguish’d
-- Speaker (Line 2)

Importance: This line establishes the nature of the apocalypse. It is easy to forget this precipitating event, because Byron offers readers so many details of what goes wrong afterwards: human behavior, geological disturbances, etc. But the poem relies on this initial event. The true cause of this disorder is the fact that the sun has...