Smallness is the starting point here. The speaker remembers hating the feeling of being a speck of dust in a vast desert, or one worm in a jar crowded with maggots. Then comes a turn: "the hourglass has turned," and minds have opened. Being small no longer feels like a problem, because even a tiny life carries infinite importance.
From there the poem shifts to images of hope and possibility. A caterpillar sits beneath a huge tree, and a child rides a giant's shoulder, so smallness starts to look like a place of safety and wonder. The imagery of birdsong, countless lives and story threads that cross but never touch suggests that everyone has their own path within a huge whole. The acorn, which could become an oak or stay a singing bush, shows that either outcome has value. The ending bursts into colour as worms become butterflies. The mood moves from low self-worth to joyful, musical celebration, with a gentle, uplifting sense of growth.