“Rage, rage against the dying of the light.”
— Dylan Thomas, Do not go gentle into that good night (1951)
Context
Thomas wrote this villanelle as his father was dying — a once-fierce schoolmaster losing both eyesight and vitality to old age. The poem's two refrains alternate through five tercets and resolve in a quatrain that finally drops the indirection and addresses the father directly. The line is the second refrain, returning four times to hammer the same imperative against mortality.
How the repetition works
The doubled 'Rage, rage' is epizeuxis used in the imperative mood: the repetition does not add information — it raises the pitch of a command. A single 'Rage' would be an instruction; the doubling makes it a cry. Where most epizeuxis on this site marks shock, grief, or stunned reiteration, Thomas's example shows the device escalating a directive — the grammar of a command carrying the feeling of a plea.