The speaker has come back to live in the place where they grew up, and the poem is a set of small, quiet observations about what that feels like. The spring house, once a cool place to store milk, now only "keeps" the snakes. The view from the childhood bedroom window is the same, but the line "I live in it now" suggests the speaker has not so much returned to a view as moved into the past itself.
Change and loss run through the details. A walnut sprout that the children once tried to kill with a frisbee has grown into a tree, and now the speaker eats in its shade. Cattails are choked by tearthumb, a thorny, invasive plant. The last line, "the purpose-driven life," drops in without comment, and it reads as dry, gentle irony: the plants simply crowd and spread, with no plan beyond growing.
The mood is calm, wry, and a little wistful. The speaker seems at ease with time's slow work, even amused by it.