The voice Adrienne Rich uses in her poem, "Song," is one of self-awareness on the part of the speaker.
"Voice" is a literary element that is sometimes difficult to understand. It is not the mood, or the author's tone. It is, rather, the persona created in the writing—the poem—in which the author has developed the poem's voice. It should not be confused with the author's ideas or feelings, which would be the tone. Here are two definitions that may help:
Voice is associated with the basic vision of a writer, her general attitude toward the world.
It is a convention in poetry that the speaker is not the same individual as the historical author of the poem.
So for Adrienne Rich's poem, "Song," the voice I "hear" is that of a woman who seems to have been told that she is lonely. (Remember, this is not the author speaking, but the woman she has created on paper.) The descriptions the speaker presents may serve as examples for her listener to the contrary: loneliness is not a part of this woman.
The speaker is challenging the concept of loneliness, and she is positive in the presentation of her "defense."
The speaker defines what loneliness is NOT, in her life. She speaks of the freedom and beauty of flying in a plane across the Rocky Mountains toward an ocean.
She then describes a woman who drives through many towns and chooses not to stop and stay, knowing that if she did, then she would be lonely.
The speaker draws to mind the image of waking early when no one else is up, and snuggling in the comfort of a house "wrapped in sleep."
Finally, the speaker contemplates the vision of what might seem to be the loneliest picture of all: a row boat entrenched in the ice on a shore, as the last light fades. This sounds solemn, and yet, the old boat knows, even in those circumstances, what it is and what it is not, and despite the impression another might get of defeat or loss, the boat is personified to understand that when all else fails, there is still hope: the boat can provide the "gift" of burning—light, life and warmth.
The speaker's voice tells the reader that unless the definition of loneliness has changed, she is not lonely. She is enjoying the freedom she has, and notes that at the worst of times, there is something living in her that can dispel darkness, fear or desolation: she has a fire within.