Do not go gentle into that good night.
Old age should burn and rave at close of day;
Rage, rage against the dying of the light.
Though wise men at their end know dark is right,
Because their words had forked no lightning they
“The close of day” furthers the conceit of “night” as death and, like the first line, we get an imperative, urging the speaker’s father to not resign himself to death and instead to go out in a blaze of glory. 
 This line is the first of the ironic contrasts and juxtapositions throughout the poem. ‘Old age’ is associated with passivity and frailty, but the poet is urging his father to ‘burn’ and ‘rave’. In short, he is denying his father’s impending death. ‘Old age’ is personified as a character, suggesting that it is not physically part of his father, but has come upon him. In the mind of the speaker, he can overcome it. 
 Note the  assonant  vowels in ‘age’, ‘rave’, ‘day’ and ‘against’ and ‘rage’ in the next line. These give the poem cohesion. 
 Unlike the first line though, the metre conforms to the more traditional  iambic pentameter , which is works well with the  villanelle form . This may be ironic, as, while the speaker demands his father to “burn and rave,” the speaker himself reverts to a more measured style, suggesting a latent insecurity within his demands. Furthermore, the short vowel sounds and stresses of the first line is replaced with longer, more sonorous sounds, compounded with the assonance of “age,” “rave,” and “day,” creating phonetic counterpoint and ‘opening’ the poem out. Indeed, the pattern of long and short vowels throughout the poem is reminiscent of breathing, a breathing which is symbolically snuffed out in the final line. 

Do Not Go Gentle Into That Good Night