Final answer:
The poem uses the metaphor of a potter's wheel to symbolize our lives.
Step-by-step explanation:
In the last line of the poem, "clay" is a symbol for our lives. The line suggests that our lives are molded and shaped just like clay on a potter's wheel. Browning uses the metaphor of the potter's wheel to convey the idea that time spins fast and our lives are passive, meaning that we are not in control of the passage of time.
Learn more about symbolism in literature