Have you ever listened to a gospel choir in concert? The sound FILLS the room. It sends shivers down your spine, brings tears to your eyes, and makes you forget about everything else but the music.
We like to think of this poem as just that sort of sound. Sure, it starts out with just one voice, singing (or, if we're being precise, speaking) but by the time we get to the first refrain, it starts to sound like there's more than one voice involved here. And by the time that our speaker starts to address the problems of other folks in Stanza 3, she's already dealing with the whole community. It's safe to assume that she's no longer talking to herself in bed at night. She's got an audience. And from the sound of things, they're taking an active part in creating the refrains of the poem.
Try reading this poem all by yourself. Then try reading it with a few of your friends. You'll see what we mean. The refrains are meant to be choral pieces. They just sound better when a whole bunch of people are speaking along together. And that's part of the hopeful message of this poem. If you imagine the refrain being spoken by a choir of voices, then the poem itself is already moving outside the spaces of isolation and alone-ness that the speaker so hates. Nifty, huh?