The Chimney Sweeper (Songs of Innocence)
How we cite our quotes:
As Tom was a-sleeping, he had such a sight—
That thousands of sweepers, Dick, Joe, Ned, and Jack,
Were all of them locked up in coffins of black. (10-12)
The speaker again reiterates the idea that children employed as chimney sweepers are dead in some way (their innocence is gone, that's for sure). The rhyme on "Jack" and "black" emphasizes the connection between the black death of the coffin and the chimney sweeper named Jack.
Then naked and white, all their bags left behind,
They rise upon clouds and sport in the wind; (17-18)
The children rise on clouds, almost as if they were on their way to Heaven. In a way, they haven't been released from death, but from their horrible lives. Now, in the dream at least, they're well on their way to a happy afterlife… maybe.
And so Tom awoke; and we rose in the dark
And got with our bags and our brushes to work. (21-22)
In many ways the children are already dead. Dark doesn't just describe the absence of light, but also the condition of their lives. It recalls the "coffins of black" and suggests that children are sort of like zombies—the walking dead. Plus, the fact that "dark" kind of rhymes with "work" suggests that there is some connection between working and death. Yep, we can empathize with that one.