You'd be hard pressed to find a more consistent sounding poet than Wallace Stevens. His modern, meditative brand of free verse is one of the main things people recognize about him. His poems sound like they're being spoken aloud by a snowy haired man who's lived a long and interesting life. In this poem, Stevens' language almost never clanks. Even when he talks about violence, the sound of his words stays measured and calm.
When talking about modern poetry, Stevens says that poetry must "think about war/ And it has to find what will suffice" (9-10). Notice how he doesn't say that poetry needs to picture "the stench of putrid corpses strewn across a bloody battlefield." No, Stevens keeps the sound of this poem very calm and very meditative, almost in a Zen sort of way. Even when he does play with sound, it's designed to soothe the reader's ear.
Check out the first six lines; maybe read 'em out loud to yourself. Go ahead. No one's looking. Hear something? It should be the soft sweep of a silvery stream of S sounds, slipping off your spoken syllables. That, folks, is consonance at work. The steady S sounds (in "suffice," "always," "scene," "set," "was," "script," "else," and "souvenir") set the scene with a calm and soothing undertone. Overall, Stevens keeps this poem calm because for him, the point of modern poetry is to help people find peace and "satisfaction" (26) in a world torn apart by conflict and grief.