what is the purpose of poetry ?

Poetry is an art form & hence there is a definite involvement of two parties; the poet & the listener. The motivations of the two parties may or may match to an extent. Ironically, however the purpose may even be contradictory. Let us understand this distinctly.
From the perspective of the creator, the poet, poetry is an evolution of a technology of communication. We normally communicate far more aggressively with text or speech. We force the person to listen to our point of view. Poetry has no such aspiration. The poetry is a mellowed down communication as it is an open proposal that people may or may not buy. Someone may like the words, the expressions, the rhythm or alliteration whereas someone else may like only the context. At a human level an emergence of poetry in is a mark of his ideological evolution of the means & measure he adopts to think, execute that thinking. Whereas in a human dialogue there is a planned communication in response to any situation or context or the purpose, poetry may come out of context & worded irrespective of who the listener might be. That is a certain qualification to be monologue. People who enter the phase of monologue are obviously the people who are done with the dialogue. But a monologue that is published must have a vitality of being read & heard despite that being not a specific communication with respect to the poet.
From the reader’s or listener’s point of view, poetry is a domain of subtlety. At the same time it is an arena of open communication. There is a lot one could derive on one’s own. To the audience, therefore poetry is a an opportunity of self-intellectualization or provocation for self-literature.