Three short lines, and the whole poem is a single glimpse: a worm, shown in a little picture hanging in the speaker's office. The wording is tight and a bit broken, as if the speaker is noticing the image rather than building an argument about it. "All in dirt" comes first, so the worm is described by what surrounds it before we even learn what it is.
The poem never says how the speaker feels, which is part of its charm. Judging by the setup, the picture seems to be something the speaker passes or sits near every day, and the poem hints at a quiet contrast between the worm's earthy, buried world and the tidy indoor setting of an office. The worm is both framed and cut off from its surroundings, like something small and ordinary that has been set on display.
The mood is calm, wry, and observant. There is a faint humor in the plainness, and a gentle sense that even a tiny, humble thing can catch our attention and make us pause in the middle of a workday.