Why?
Poetry makes up the majority of the Hebrew scriptures, this sparks the subtle question why or even why not? Answering this question is not the easiest, for two reasons. Firstly, we are not God, nor are we going to hold a conversation with him anytime soon on the matter. Secondly, if one stretches too far, one can begin to unravel the idea which Paul informed Timothy that all scripture is God breathed.
The second issue comes into play when you begin to understand the social aspects of how stories in the ancient world were passed down orally. What this does if taken too far is to make what we have in the bible not God breathed directly, but rather “telephoned” down through time until someone wrote it down after being passed orally and possibly corrupted.
The first is not as unhelpful as we might think. Poetry is not some dead art, nor was it only contained with in Hebrew scripture. So if we take humans to be in some fashion “God Images”, our emotions etc are fashioned after his, our language is fashioned by him, our social interaction determined by his nature. Then it is not too far of a stretch to say that some how poetry, speaks to the heart of God. In our modern world most of poetry has lost all subtlety, but if you look to perhaps the romantic period we see a beautiful use of the pen to create dreamy lines that connect with the heart in a way that most prose cannot. While prose and composition can keep a reader riveted, and over time manipulate the emotions, poems can achieve such in only a few words or lines.
So why poetry? It is not out of the question that it was breathed by God to help his people remember it more easily as they passed the traditions down. Perhaps more deeply though poetry is a way which we are able to release our hearts, to open the depths of our insides and speak that which is beautiful or ugly in ways that regular speech or prose cannot express or contain.
