In "A Defence of Poetry," Shelley opines that poets are the "unacknowledged legislators of the world." This famous excerpt from the essay illustrates Shelley's views on the art of poetry and why it is an important literary form.

Since Shelley is considered a poet of the Romantic movement, his essay is to be read within this context; however, many of Shelley's arguments in the essay can be applied universally to poetry as a whole. For instance, Shelley talks about the importance of language in poetry and, in turn, why the English language needs poetry. Shelley also states that poetry is something that is innate in all human beings—that the ability to express one's thoughts, emotions, and experiences through poetic medium is essential to speaking any language.

Shelley also expresses his belief that poetry is a medium that can affect political and social change. The postmodern American poet Amiri Baraka would later echo this sentiment by stating, "Art and social commentary cannot be divorced." Shelley, who wrote Romantic poetry, was not known for political discourse or social commentary like his peer William Blake, but he understood poetry's power as a medium.