Final answer:
Thoreau uses imagery to portray time as a flowing stream, suggesting its continuous, unceasing nature and emphasizing a life lived deliberately, in tune with the essentials and natural rhythm.
Step-by-step explanation:
In the excerpt from Walden, "Time is but the stream," Thoreau most likely uses imagery to portray time as a flowing stream.
This metaphor suggests that time is continuous and ever-moving, similar to a stream's constant flow.
In Walden, Thoreau often reflects on the concept of time, emphasizing the importance of living deliberately and focusing on the essentials of life.
He explores the theme using nature as an analogy, highlighting how his simplified lifestyle on Walden Pond allows him to experience time more profoundly and with greater awareness, as opposed to the busy distractions of society which might cause one to lose touch with the natural passage of time.