Waking early, the speaker slips out of an ordinary sense of self and into something fluid. The poem moves in short, quiet steps: "up early," "like water," then the odd phrase "being myself only," which sounds simple but feels like a small act of surrender. To be only yourself, here, seems to mean letting go of the effort to be anything more.
The title, "Multiplication," hints at the puzzle in the parenthesis: a "mathematics / that I cannot understand." The speaker seems to become more than one thing at once, both a person and the rain, and admits they can't explain how. The poem doesn't try to solve it.
By the end, the speaker is "the rain coming into my house," as if the boundary between inside and outside has dissolved. The mood is calm, curious, and receptive. The final words, "being open," read like both a description and a gentle wish.