Silence is the only subject here, but it keeps changing shape. The opening lines pile up familiar kinds: the stillness of stone, the quiet of night, the "dead silence" of a room where no one speaks. Then the mood tightens. Silence before a storm is full of waiting, and "held breath" and "a scream in space" turn it into something strained, even frightening. A scream with no sound, and no one to hear it, is a striking picture of how loud quiet can be.
The middle lines widen out. Silence comes "before anything" and "after everything," like the start and end of time. The single rose is a small, calm image, almost a pause within the poem. Then the ending turns personal. The speaker has been asking questions and getting nothing back. All the earlier silences lead to this one, and it hurts most. The mood moves from eerie to heavy to quietly sad, as the speaker faces the silence of someone who won't answer.