Both of these poems, like many of Shelley's poems, start off by describing a natural event and then use this event as a way to discuss the way that nature can powerfully impact and transform the lives of men. Throughout both poems, Shelley hopes and dreams of what his poetry could do, if he were able to harness the power of the West Wind and then the beauty of the skylark's song. Note the following examples, that directly relate to hope and aspiration:
Teach me half the gladness
That thy brain must know,
Such harmonious madness
From my lips would flow
The world should listen then--as I am listening now.
Here, Shelley expresses his desire to learn from the skylark and its beauty, so that his poetry can somehow be able to capture and share the beauty of the skylark's song and make man stop and listen to the beauty and transforming power of nature.
Drive my dead thoughts over the universe
Like withered leaves to quicken a new birth!
And, by the incantation of this verse,
Scatter, as from an unextinguished hearth
Ashes and sparks, my words among mankind!
Here again we see Shelley aspiring to capture or harness the power of nature to spread his words and his poetry throughout all of mankind. In a powerful image, he imagines his words like dead leaves being scattered throughout the planet so that they might "quicken a new birth."
In these two poems therefore we can clearly see the way in which Shelley aspires to use the example of nature in his work, and the hope that by so doing, he can improve both mankind and the world.