Rowan Williams, former Archbishop of Canterbury, delivered a lecture on July 27 in which he thoroughly posits the constitution of hymnody vis a vis poetry. Worth a look.
http://www.praytellblog.com/index.php/2015/08/12/hymns-poems-songs-the-lyrical-and-the-liturgical/
http://www.praytellblog.com/index.php/2015/08/12/hymns-poems-songs-the-lyrical-and-the-liturgical/