The poem "The Cloud" by Percy Bysshe Shelley employs an extended metaphor, as it compares a cloud to life throughout the whole poem.
The cloud is meant to stand for the cycle of nature, or the unending cycle of life. Through the many cycles and transformations that the cloud endures, Shelley wants to represent the never ending cycle of birth, death and rebirth that all beings on Earth go through. The poem, therefore, focuses on the mutability of nature as the only constant in the physical world. Moreover, this allows the author to also employ the cloud as a symbol of the many changes that humans undergo throughout their lives.