A poem is a rite; hence its formal and ritualistic character. Its use of language is deliberately and ostentatiously different from talk. Even when it employs the diction and rhythms of conversation, it employs them as a deliberate informality, presupposing the norm with which they are intended to contrast.
The form of a rite must be beautiful, exhibiting, for example, balance, closure and aptness to that which it is the form of. It is over this last quality of aptness that most of our aesthetic quarrels arise, and must arise, whenever our sacred and profane worlds differ.
–W. H. Auden, “Making, Knowing and Judging”