As all the Heavens were a Bell, And Being, but an Ear, (lines 13-14)
This poem contrasts the incredibly huge with the incredibly small. The largeness of the "Heavens" is placed beside the smallness of a human ear. We're just a tiny speck in a massive, reverberating universe. Makes you feel a bit humble, doesn't it?
And then a Plank in Reason, broke, And I dropped down, and down– And hit a World, at every plunge, And Finished knowing–then– (lines 17-20)
We thought things couldn't possibly get bigger than the "Heavens," but now she brings in multiple "Worlds." Sounds a bit like the idea of parallel universes. She could mean something like other states of consciousness that we can't even imagine. This is a very trippy poem.