Which poem relies most heavily on a refrain to express its themes?

The poem that relies most heavily on a refrain to express its themes is "Do Not Go Gentle into That Good Night" by Dylan Thomas. In this villanelle, the repeated lines "Do not go gentle into that good night" and "Rage, rage against the dying of the light" serve as powerful refrains that encapsulate the poem's themes of resistance against death and the struggle for life. The use of refrain is central to the structure and emotional impact of the poem.