huh, the last sentence of my post got dropped; put it back now.
No, they're not mantras.
The easy answer is that rhythmicity of language is just fundamentally compelling to our minds at a very basic level, and poems are a way that we can bend and twist and revel in and celebrate with language that gets that.
There's often a "oh, you clever ... " satisfaction as a reader when the poet picks _just_ the perfect word to rhyme off and you're left almost gasping with ... something indescribable ... at how _right_ it was. It's a thing of beauty.
In translation, Hafiz: "... the Beloved / has just made such a fantastic move// that the saint is now continually/ tripping over Joy// and bursting out in laughter/ and saying "I Surrender!""
Watching someone, often someone long dead from a time and a place I can't even imagine, working within an often highly constrained form to produce something that still packs a punch -- something that can still reach out and wrench something loose inside your head, something that can communicate things that are probably ineffable -- when it happens to you, you'll know.