Hope is the thing with feathers That perches in the soul,
And sings the tune without the words,
And never stops at all,
And sweetest in the gale is heard;
And sore must be the storm
That could abash the little bird
That kept so many warm.
I’ve heard it in the chillest land,
And on the strangest sea;
Yet, never, in extremity,
It asked a crumb of me

what is the metaphor

and what is the comparison