The speaker is worn down by work that is dull and perhaps harmful, and admits to doing it dully, as if the boredom has seeped into them. The poem's answer is to leave. They head into the country, hoping that walking might act as a kind of medicine, which the title, "Open-air cure," suggests.
The mood is quiet, tired, and a little hopeful. The phrase "the old marl of knowing / how I ought to walk" is slightly strange. Marl is a soft, clay-rich soil, so the speaker seems to be stepping on ground that holds old, half-forgotten knowledge about how to move through the world. The wish "to be repaired" makes the speaker sound like something damaged rather than simply unhappy. The last lines are modest: they ask for "any humor" and "any other time," meaning any mood or any pace that differs from the grind. The speaker isn't demanding joy, only a break from the sameness of work.