As all the Heavens were a Bell, And Being, but an Ear,
The "Space" from line 12 turns into the "Heavens" that ring like a bell. Dickinson has zoomed way, way out from the funeral scene.
"Being" is a generic term for existence. We say "human beings," for example, to refer to human existence. If Being is an ear, that makes us into passive receivers of the noise of the universe. We can't control what we hear.
The tolling of the bell is a repetitive sound that reminds us of the "treading–treading" of the first stanza or the "beating–beating" of the second.
And I, and Silence, some strange Race Wrecked, solitary, here–
These are difficult lines. In lines 13-14, the speaker described being a passive listener to the great big bell in the sky. Now she expands on the feeling of isolation that goes along with the idea of a big, empty world filled only by sound.
She says that she and Silence belong to the same "Race," or type of individual. We don't know why Silence would be in a world filled with the sound of a bell, but Silence is the passive or negative side of sound. Both the speaker and Silence are passive and empty.
So, we've got quite a party developing here. The speaker and Silence are hanging out, alone ("solitary"), as if they have been "wrecked" on an island.
To highlight the fact that we don't know where the heck they are, she says they are "here." Naturally, this information won't be too helpful to the search-and-rescue party.