A big old oak is being cut down, and the poem watches it happen in just a few sparse lines. The tree "rocks" as the saw bites in, and the word works two ways: it sways, but it also sounds like something being shaken loose. The oak is "taken by fire and exhaust," so the clean smell of wood gives way to smoke and engine fumes.
The second stanza turns bitter. An engine "promises / the least world," which suggests that machines offer us a smaller, poorer version of what we already had. The speaker seems to be saying that convenience and power come at a cost to the living world around us.
The last stanza points ahead to a house built from the felled tree, one that will be "very hard to love." The judging by the imagery, the speaker feels grief and unease, and perhaps guilt about how people take what they need. The mood is quiet, stark, and mournful, with no big outcry, just a cold sense of loss.