This apparently simple poem is more complex than it seems at first glance. By using the imperative in the first two stanzas, Wordsworth introduces ambiguity into the opening lines: is he addressing us as readers or is he talking to himself in the lonely Highlands vale—or is he doing both? It is up to the reader to decide, but the deep interiority of the poem and the switch to the first-person pronoun in the last two stanzas supports an interpretation of Wordsworth addressing both the reader he invites into the scene and himself. Like Frost in "The Road Less Traveled," the narrator in this line is at a moment of decision: should he "stop" in his journey or "gently [quietly] pass" by the reaping woman? That this is an important decision to him (perhaps as in "The Road Less Traveled" the narrator has places to go?) is indicated by the exclamation point at the end of the line.
By the next stanza, the narrator has clearly made his decision (or had it made for him by the beauty of the arresting, melancholy song), for he writes the following:
Alone she cuts and binds the grain,
And sings a melancholy strain;
O listen! for the Vale profound
Is overflowing with the sound.
The narrator has made his choice. He has stopped, and invites—nay, implores and commands us—to join him, to "listen!" The solitary reaper's song is now, for this moment, the most important thing in the world to the narrator: that he is deeply emotionally riveted to the spot is emphasized by the "O" before listen and the second exclamation point after the phrase, which stops us as the song has stopped the traveler.