When you answer this question, you must remember that theme is the broad message or moral of a piece of literature. Think about the big idea of the text. Try to infer what the author wants the reader to think about or learn.
Longfellow’s poem is a statement about slavery and freedom. In the first and last stanza, you learn that the subject of the poem is a dying slave. He is “in the mist of shadow and sleep” and he doesn’t “feel the driver’s whip”. What the slave does feel is his homeland, liberation and triumph while he is in a dream-like state during the process of dying. He is remembering his homeland, his life before slavery, his wife, his children and his horse. This makes the dying slave feel free within his soul. Longfellow’s poem reminds us that the one place where all humans can remain free is within their mind. This is a universal theme and it can be found within many other pieces of literature.