Final answer:
The most significant line from "The Raven" contributing to its eerie effect is the final stanza, where the motif of 'nevermore' deepens the mood of despair and inevitability, accentuated by the dark, persistent imagery and symbolism.
Step-by-step explanation:
The line from Edgar Allan Poe's "The Raven" that most contributes to the eerie, hypnotic single effect of the poem could arguably be the final stanza, where the nevermore of the raven has its full impact:
'And the raven, never flitting, still is sitting, still is sitting
On the pallid bust of Pallas just above my chamber door;
And his eyes have all the seeming of a demon's that is dreaming,
And the lamp-light o’er him streaming throws his shadow on the floor;
And my soul from out that shadow that lies floating on the floor
Shall be lifted - nevermore!'
This stanza encapsulates the despair and sense of inevitability that permeates the poem, reinforced by the relentless repetition of the word 'nevermore,' which has become nearly synonymous with the raven itself. The imagery of the raven still sitting, the references to Pallas (a symbol of wisdom), and the demon-like eyes contribute to a sense of an inescapable curse or doom. The shadow on the floor symbolizes the weight and darkness of the narrator's grief, suggesting it will never leave him thus amplifying the poem's hypnotic single effect.