– and then it was
There interposed a Fly –
Back to the fly. “Interposed” means it came between two things. In the next stanza we see that it came between the speaker and the light source in the room — but it also seems to “come between” the speaker and a peaceful death.
It also denotes the importance of the fly. The fly interrupts the persona when they are sorting out their will. Something that would almost leave a legacy is disrupted by something as petty and annoying as a fly.
Why a fly? Flies notoriously feed on corpses, so in one sense this may just be a reminder of the ugly reality of death. Flies are also thought of as common, lowly creatures, so the appearance of this one contrasts ironically with the expected presence of “the King” (God) in the room.
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