For one, the diction of the title brought to me this idea of “the pearly gates” finally closing. I see this as a connotation for the afterlife. The realm for the dead has closed, meaning that it has reached it maximum capacity. In other words, I see the title as a way of seeing once the human race has become extinct.
This was further reinforced by the third line:
but it was already gone,
no human sound…
I feel that this means that humans have perished the earth. Bringing back this idea of global warming, this poem takes place in a world that has been pushed past capacity — it has been mined, drilled, deforested, and exploited as much as possible. Consequently, the earth is now nothing but a vast wasteland. It is so barren that “the wind had nothing to rub a whisper from.”
So much so that life on earth has been reduced to “just silence \ rising over the valley \ deep and wide as a glacier.” The simile of a glacier makes me feel that the only thing that is left is cold and hollow, drifting aimlessly in a barren planet. Recalling events such as the sinking of the Titanic, the glacier brings a feeling of catastrophe. It’s also a bit funny, since glaciers are fading as global climate change advances. Once the world can no longer take the current exploitation rate, glaciers will rise and humans will fall.