Why does the poet use the extended metaphor of the caged bird in his poem "Sympathy" ?

Why does the poet use the extended metaphor of the caged bird in his poem "Sympathy"?. What does the metaphor represent? What is its purpose in the poem? Write a brief informative/ explanatory essay that explains how this extended metaphor affects the meaning and tone of the poem. How does it help to develop the theme? Begin with a clear topic sentence, and show a clear progression of an idea, include information about how the poet's word choice, including his use of figurative language and connotations, impacts the meaning and tone of the poem. Cite specific textual evidence in your response.