What does the metaphor in these lines from the passage signify?

when yellow leaves, or none, or few, do hang
upon those boughs which shake against the cold,
bare ruin’d choirs, where late the sweet birds sang.

This excerpt is from “the poet” by alfred, lord tennyson. the poem describes a poet's consciousness and perception. which three lines suggest the richness of a poet's thoughts? thus truth was multiplied on truth, [the world like one great garden show'd,] and thro' the wreaths of floating dark upcurl'd, rare sunrise flow'd. [and freedom rear'd in that august sunrise] her beautiful bold brow, when rites and forms before his burning eyes melted like snow. [there was no blood upon her maiden robes] sunn'd by those orient skies; but round about the circles of the globes of her keen eyes and in her raiment's hem was traced in flame wisdom, a name to shake [all evil dreams of power--a sacred name.] and when she spake, [her words did gather thunder as they ran,] and as the lightning to the thunder which follows it, riving the spirit of man, making earth wonder, so was their meaning to her words. no sword of wrath her right arm whirl'd, [ but one poor poet's scroll, and with 'his' word] she shook the world.