The central theme in “To a Skylark” is the power of nature. Shelley primarily uses water imagery to convey this concept. There are descriptions of literal rain, such as “vernal showers” (Line 56) that fall on “rain-awakened flowers” (Line 58). Rain is also used to describe music, as seen in the passage “showers a rain of melody” (Line 35). The power of nature increases from gentle showers to more excessive bodies of water. For instance, both the moon and music exude water in excess, or superflux. The “moon rains out her beams, and Heaven is overflowed” (Line 30) and a maiden makes “music sweet as love, which overflows her bower” (Line 45). Both passages use diction related to flooding—“overflow.” This implies the awesome power that belongs to water. However, moonbeams and music are both intangible—that is, they will not cause destruction like a literal flood. Shelley conveys their intangible power by comparing them to a power that can be understood in a tangible, physical way.

The skylark’s song is also described in water-based terms. Humans are unable to match the skylark as it “panted forth a flood of rapture so divine” (Line 65).