Get out the microscope, because we’re going through this poem line-by-line.
Lines 13-14
And by came an angel who had a bright key,
And he opened the coffins and set them all free;
The dismal picture in Tom's dream doesn't last. And thank goodness.
Now, an angel shows up with a "bright key" and lets all the sweepers go free.
This could be a reference to Matthew 16:19, the verse in which Jesus gives Peter the keys to the kingdom of heaven. Maybe Peter's that angel, coming down to give these kiddos a much-deserved ticket to the Promised Land.
In any case, the imagery here is a nice, uplifting contrast to those creepy, suffocating, black coffins. But still—the imagery here is all about death.
So is he saying that death is the only way out of this awful, sweepy mess?