Several stanzas of this poem are explicitly about eating and drinking, and the speaker clearly has strongly held opinions about the right and wrong way to eat, what to eat and when, and how to behave at the dinner table. In Western poetry, the act of eating together is often symbolic of the Last Supper of the Christian tradition: the last meal Jesus ate with his disciples before he died. Fruit and gardens pack a big symbolic punch in the Judeo-Christian tradition (Garden of Eden and the fruit from the Tree of Knowledge, anyone?) so whenever you see a poem with fruit in a garden in the Western literary tradition, stop and think about if there's some kind of tacit allusion to the Garden of Eden hidden away in there.
The cloister here is hardly a paradise, and the monks at dinner hardly seem like the disciples at the last supper... unless the speaker is meant to represent the serpent in the Garden of Eden, or Judas at the Last Supper. What do you think?