The title is French for "staircase wit," the phrase for the clever comeback you think of only after you've left the room and are already on the stairs. The poem plays with that idea. Its stairs become "a place / to practice going to / the bottom of things," a spot for rehearsing what we should have said, or for digging down into what we really mean.
Then the poem shifts to something small and living: a wren, apparently swearing "freely" at an odd robin. The wren seems to be everything the speaker isn't. It doesn't wait for the perfect line; it just lets rip, in the moment, at whoever turns up. The phrase "difficult ground" suggests the wren's low, rough territory, but it may also hint at how hard honest speech can be.
The mood is quiet, wry and a little wistful. The speaker seems to watch the bird with amused envy, caught between private second-guessing and the easy bluntness of nature.