Most of "Seeing" is a quiet list of things the speaker has learned to notice: light stopping on the side of a white house, shadows from bare trees, the colors of clouds, what moonlight does to snow. The sentences are often fragments, so the poem feels like a mind collecting images one by one rather than building an argument.
The middle turns personal. The speaker admits to passing a sawmill every day without really seeing it, until it appeared in a picture on a wall, down to every log and wisp of smoke. That suggests the poem is partly about how art teaches us to look. The ending shifts the mood. The house that "anchored the old farm" is where a neighbor died last winter, and the calm observation takes on loss. Seeing, the poem implies, can be a way of paying attention to what we might otherwise lose. The tone is steady and reflective, with a quiet sadness at the close.