The speaker pictures time as a river and imagines standing in it, fully underwater, while the days pass through them. In the bending, flickering light, they glimpse a way of seeing that cuts past surface appearances to something deeper. What they find there is a kind of nothingness, though they quickly correct themselves: it is less a void than "the presence of an absence," something felt precisely because it is missing. The line about the self being "only a dream" sounds both calm and unsettling.
The poem then turns from abstraction to something rawer. The real tragedy, the speaker says, is whatever can't be put into words. Everything else is a "beautiful, hideous mess," and the final, isolated line, "is life," lands quietly and plainly. The mood is reflective and dreamy, with a hint of sadness, but it ends in acceptance. The broken, scattered layout on the page mirrors the flowing, shifting feeling of the river.