Why are structure and rhythm important parts of poetry?

Let's first establish what these two literary devices are: 

Structure is the form that the poem adheres to by using specific stanzas, meter schemes, rhyme schemes, and subject content. The types of structure are incredibly diverse both across and within cultures. Examples include Epic Poem, Free Verse, and Petrarchan Sonnet.

Rhythm is the meter of a poem, or the pattern of stressed and unstressed syllables in each line. Meter is composed of feet, or small groups of syllables, which repeat for a certain number of times depending on the type of meter. Examples include Iambic Pentameter, Free Verse, Blank Verse. 

In a poem, the structure and rhythm work together to produce emphasis for certain parts of the poem. As a result, different words and concepts become the reader's focus as opposed to others, developing deeper literal and figurative meaning.