The lines from this excerpt that are refrains are:
1) "Do not go gentle into that good night"
2) "Rage, rage against the dying of the light."
Refrain, as a poetic device, is the repetition of a line, words, or phrases in a poem. Using refrains in a poem help to its rhyme. Refrains also emphasize an idea by repeating the same lines or phrase several times in a poem. They are usually repeated at the end of a stanza.
