The speaker begins with an exclamation, "o," that sounds half like a wish and half like a sigh. What they long for is hardly comfortable: to live on coal and "our own thin milk." Coal is fuel, not food, and thin milk suggests something watery and not nourishing enough. Together they paint a picture of scraping by, getting little from very little. The "our" hints that the speaker isn't alone, perhaps sharing this hardship with someone else, though the poem doesn't say who.
The second stanza turns inward. Bad weather and rot, both natural forces of decay, are placed inside the body: a storm in the belly, anger festering in the heart. The speaker's hunger and their emotions blur together. The mood is bleak, cramped and resentful, but also compressed and controlled. With so few words, the poem makes the anger feel stored up and slow-burning rather than explosive.