Time
Time is the central theme of the poem, the “force” that the speaker continuously references. The speaker is fascinated by how it brings both life and death. Furthermore, the speaker repeatedly notes the twin effect that time has on nature and the human body, with everything from a flower to a coursing river just as affected by it as people are. By not naming time explicitly until the fourth stanza, Thomas allows readers to draw these connections on their own. In the fourth stanza, time is finally personified as a vampire-like figure whose “lips” feed off the blood of love.
Nature and humanity
To the speaker, the human body is a direct mirror of the nature that surrounds it. Both are at once sustained and destroyed by the same force: time. The poem is structured as a series of metaphors and comparisons that link the speaker's body to nature. He likens flowers blooming to his youth, a stream to his blood, and wind to the shroud a body is buried in. Nature and humanity are thus inseparable.
Expression
A third theme of the poem is expression: the act of speaking or writing a poem itself. The speaker repeatedly states that he is “dumb to tell”: too astonished and perhaps intimidated to properly express his feelings regarding the power of time. The paradox, of course, is that the poem does precisely that, illustrating these feelings eloquently.
