Quote from : The Story of the Hymns and Tunes Book

It is natural to speak of hymns as "poems," indiscriminately, for they have the same structure. But a hymn is not necessarily a poem, while a poem that can be sung as a hymn is something more than a poem. Imagination makes poems; devotion makes hymns. There can be poetry without emotion, but a hymn never. A poem may argue; a hymn must not. In short to be a hymn, what is written must express spiritual feelings and desires. The music of faith, hope and charity will be somewhere in its strain.