Starting from the familiar phrase "ashes to ashes, dust to dust," the poem follows what happens to everything that disappears: city walls, a guard captain, a book, a tree. All of it becomes dust, tiny specks that nobody notices until they are gone. The speaker seems calm rather than frightened. Even the tree might have been proud or worn down, and the poem suggests it accepted its time either way.
The middle of the poem describes decay slowly, as light turns to streaks and chips become cracks and then holes. Those holes appear in walls, people, words, and the whole realm, and dust fills them. The ending is quietly sad. Dust is seen but not acknowledged, swept away only to settle again somewhere else. The repeated words and the final lone "again" make the cycle feel endless. The mood is gentle, resigned, and a little lonely, as if the speaker is looking at loss without protest.