The title sets the scene: someone buried alive, aware and stuck. The poem then spreads that feeling across a few strange images. The "wheel of occasions" suggests events turning round and round, a cycle of obligations the speaker can't step off, and the plain statement "I am denied liberty" makes the cost clear.
Next comes a priest "officiating in a cubical" with "not one little door." The cubicle is a small, boxed-in space, and the missing door means no way out. The priest and his ceremony hint at a burial, or at a ritual that has hardened into confinement. The final lines are odder: the speaker has "no mind to play cards / with a root." A root belongs to the earth, and cards are a pastime, so the picture is of a grim, absurd company underground, with nothing to do and no one to talk to.
The mood is claustrophobic and darkly wry. The speaker sounds trapped, but also oddly detached, as though noticing the absurdity of it all.