A characteristic unique to poetry is rhyme scheme. Rhyme is understood as the repetition of sounding words at the end of lines both in poems and songs. As a result, they bring musicality to the poem or song in question. On the contrary, prose lacks rhyme for it is plain but has all the other characteristics mentioned (a narrator, a theme and punctuation).
The fact is that poetry is used for the poem to causa a pleasant effect in the reader when hearing it and also to help both the reader and the listener to remember it easily.