Rilke said, "For poetry isn't, as people imagine, merely feelings (these come soon enough); it is experiences. To write one line, a man ought to see many cities, people, and things; he must learn and know animals and the way of birds in the air, and how little flowers open in the morning. One must be able to think back the way to unknown places...and to partings long foreseen, to days of childhood...and to parents...to days on the sea...to nights of travel...and one must have memories of many nights of love, no two alike...and the screams of women in childbed...one must have sat by the dead in a room with open windows....But it is not enough to have memories. One must be able to forget them and have vast patience until they come again...and when they become blood within us, and glances and gestures...then first it can happen that in a rare hour the first world of a verse may arise and come forth." (Malte, pp 25-27)
Poetry provides an experience; it is physical. The five senses are activated. Sometimes people think it is about expressing feelings, but I agree with Rilke that it is about expressing experience. In this quote, he says that one must have integrated the experience so that it has become part of yourself, in your blood, glances and gestures. It is, in other words, experience that changes you. (Writing assignment: write about something that changed you).
Very good poems can change you.
Read this essay, Mark Doty writing about Rilke's poem, "Archaic Torso of Apollo."