The first three lines of “Do Not Go Gentle Into That Good Night” establish the poem’s themes and its form. This is a poem about death, and it makes a passionate argument about how people can face death with dignity.
The speaker lays out the essence of this argument in the poem’s opening lines. He or she doesn’t think that people should “go gentle into that good night.” The speaker uses this phrase as a metaphor for dying. That is, the speaker compares the acceptance of death to the peaceful transition from day to night. The speaker argues against this acceptance, saying that people should always choose light, or life, over the darkness of death. The word "good" in the phrase "good night" is ironic: the speaker definitely doesn’t think death is a good thing! The strong consonance in the line—the /n/ and /t/ sounds in "Do not go gentle into that good night"—underscores the speaker’s bristling, fierce passion: his or her fighting spirit.
So, in the poem’s first line, the speaker says that people shouldn’t just give up when they face death; the speaker doesn’t want them to be “gentle” about it. Instead, as the speaker clarifies in the next two lines, he or she wants people to fight bravely and fiercely against death. Old people should “burn and rave” when they face death—which the speaker calls “the close of day” (using the same metaphor as the previous line: death is like darkness).
The speaker emphasizes the passion that he or she wants to see by using another metaphor: the speaker wants “old age” to “burn.” In other words, the speaker wants old people to be as passionate as fire when they fight against death. The speaker underlines this in line 3, where he or she tells them to “Rage, rage against the dying of the light.” The repetition of the word “rage”—an instance of epizeuxis—underscores the intensity that the speaker hopes to cultivate against death, here represented through another metaphor that uses darkness and light: “the dying of the light.” Further, the assonant long /i/ sound that links together “dying” and “light” gets at one of the problems the poem will wrestle with: no matter how hard one fights, death is still inevitable. “[D]ying” and “light” are linked together.
“Do Not Go Gentle into That Good Night” is a villanelle—a strictly patterned kind of formal poetry. Villanelles are written in tercets and follow an interlocking, repetitive structure. The first stanza of a villanelle is very important because its first and third lines establish the two refrains that will repeat throughout the poem. Here, those two lines are "Do not go gentle into that good night" and "Rage, rage against the dying of the light." This specific villanelle is also written in iambic pentameter and follows the standard rhyme scheme for a villanelle, ABA.
“Do Not Go Gentle Into That Good Night” is one of the most famous villanelles in English; it’s often the poem that people offer as an example of the form. But every so often the speaker’s passion gets a little out of hand, and the poem slips out of its own boundaries. For instance, a spondee opens line 3 instead of an iamb: “Rage, rage.” The speaker’s passion overflows here, introducing a little strain into the poem’s otherwise masterful form. Elsewhere, the speaker's control is fully on display: for example, each of the poem's first three lines are end-stopped, which makes them feel all the more definite, all the more full of conviction.