How to comment on the 3rd stanza of the poem chimney sweeper from the songs of innocence

The third stanza is as follows:

And so he was quiet; and that very night,
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.

The speaker is relating a dream that Tom had one night. The imagery is dark and full of death. There is a rhyme scheme ABAB.