Poetry is language used with personal intensity. It is not, as so many suppose, decorative speech. Poets tell us what our eyes, blurred with too much gawking, and our ears, dulled with too much chatter, miss around and within us. Poets use words to drag us into the depths of reality itself. They do it not by reporting how life is, but by pushing-pulling us into the middle of it. Poetry grabs for the jugular. Far from being cosmetic language, it is intenstinal. It is root language. Poetry doesn’t so much tell us something we never knew as bring us into recognition what is latent, forgotten, overlooked, or suppressed. The Psalms text is almost entirely in this kind of language. Knowing this, we will not be looking here primarily for ideas about God, or for direction in moral conduct. We will expect, rather, to find the experience of being human before God exposed and sharpened. (Eugene H. Peterson, Answering God: The Psalms As Tools For Prayer, p.11-12)
Good stuff. This is one reason that I get tired of people using Psalm 137:8-10 (dashing infants against rocks) as an argument against a loving God (the other reason, I think, is the context of the chapter).