The speaker's role in "Poetry" by Marianne Moore is to define what poetry or, to be specific, good poetry ought to be.

In the longer version of "Poetry" in particular, Moore attacks what she calls "half poets," which one takes to mean those modern poets who write about all kinds of trivial things without making them truly poetic.

The speaker doesn't think there's anything wrong with writing poems about such trivia, whether it's business documents or school books. But she certainly does think there's something wrong about taking trivia and turning it into poetry that is overintellectualized and incomprehensible.

In the longer version of the poem, Moore is more explicitly prescriptive about what constitutes good poetry. Though even here, her wish to see poems give us "imaginary gardens with real toads in them" is somewhat ambiguous, to say the least.

What Moore appears to be getting at here is that the raw materials of everyday life need to be transformed so that we look at them in a completely different way. By comparison, "half poets" simply take what's readily available and keep it trivial.