In this fine poem by cummings, the rose functions as a metaphor. The rose's slow opening in spring is presented as an analogy for the person addressed, and, specifically, for the relationship of the narrator and the person addressed. The narrator says, "you open always petal by petal myself." Is it the person opening? Or the narrator? The indeterminate nature makes the poem a shared metaphor.
The metaphor extends later in the poem, evoking fragility (in the dream of winter), and the power of beauty to move the soul (in the comment on "the voice of your eyes").