A poem's tone is expressed through the attitude or emotional state of its speaker. "Do Not Go Gentle into That God Night" has an unusual tone, being defiant towards death rather than accepting or resigned.
The conventional poem about death often urges the reader and whomever the speaker is addressing to face death with gentle acceptance as God's will and as a transition to a better place where they will be greeted by loved ones. However, the speaker in this poem angrily denounces the idea of peacefully accepting one's end.
Using apostrophe, which is the direct address of an absent person or object, the speaker tells his father not to die in a "gentle" way. Instead, he urges his father to defy death. The speaker repeats the refrain:
Rage, rage against the dying of the light.
The speaker's grief and lack of acceptance of losing his father is revealed in his tone of fierce advice to him to fight as hard as he can to stay alive. Active, fiery images communicate this defiant tone. The speaker urges his father to be like "wild men" who "caught and sang the sun in flight." He then invokes the image of
Blind eyes [that] could blaze like meteors and be gay.
By using examples of other men who fought to stay alive in fiery ways, the speaker expresses his desire that his father mount the same kind of fierce resistance.