We read poetry because the poets, like ourselves, have been haunted by the inescapable tyranny of time and death; have suffered the pain of loss, and the more wearing, continuous pain of frustration and failure; and have had moods of unlooked-for release and peace. They have known and watched in themselves and others.
Propaganda has a bad name, but its root meaning is simply to disseminate through a medium, and all writing therefore is propaganda for something. It's a seeding of the self in the consciousness of others.
How frail and ephemeral is the material substance of letters, which makes their very survival so hazardous. Print has a permanence of its own, though it may not be much worth preserving, but a letter! Conveyed by uncertain transportation, over which the sender has no control; committed to a single individual who may be careless or inappreciative; left to the mercy of future generations, of families maybe anxious to suppress the past, of the accidents of removals and house-cleanings, or of mere ignorance. How often it has been by the veriest chance that they have survived at all.
The test of literature is, I suppose, whether we ourselves live more intensely for the reading of it.