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
These are famous lines from a poem by Dylan Thomas.
These lines are delivered multiple times by Dr. Brand in Interstellar. During the end of the movie, these lines are also seen engraved on a stone at the space station.
What significance do these lines have in the movie?
It's about not giving up, but fighting for life - and survival - with all your might.
Dylan Thomas wrote the poem about his father, David John Thomas. The poem (and the lines you quote) signify Thomas' belief that those who reach old age, like his father, should not simply consent to death - rather they should fight it and ensure they live the twilight of their lives to the fullest extent they can.
Note that Thomas refers to death as the good night - he's not saying it's something to fear or it's something bad. He's simply saying that you should cling on to life for as long as you can.
When Dr. Brand uses it in Interstellar, it's symbolic of humanity's continual fight for live - their desire to not go gently in to the night, but to fight tooth and nail for survival.
It's particularly fascinating that Dr. Brand references the poem, as we later learn that he has effectively given up on "Plan A", which he didn't believe could work. But despite this, he still tried to resist going gently into the good night, keeping the spirits of his co-workers up and trying to make them believe "Plan B" (which did work), was the correct path to take (even if he himself didn't believe it). This gave them reason to live and kept them fighting and working hard (should burn and rave at close of day) to avoid humanity's end (Rage, rage against the dying of the light).
Because he knew, like Cooper, that mankind would find a way to live. He wanted them to extend the research (like extending life) as far as possible. Eventhough he lied, he knew there was a possibility to survive, sure it was not Plan A, but he knew. So that's why he didn't want them to go gently into that goodnight.
I made an account specifically so I can weigh in on this topic, as I have just written a highly in-depth analysis on this poem by Dylan Thomas. While Andrew Martin Is absolutely correct, it goes much deeper than that.
Through much research on Thomas’ youth and the relationship he had with his father, I was surprised to find out that he actually had a horrible relationship with him and wanted to get far away. Yet he still wrote a beautiful poem for him on his death bed, one that is often quoted at funerals to this day.
When analyzing poetry, one must consider who or what is the speaker, and what is it’s intention. For this particular poem, the speaker is the author himself speaking to his dying father, begging him to stay alive and keep fighting. But who does Dylan Thomas think he is? He resents his father and leaves home at an early age and doesn’t see him for YEARS...then thinks he can just walk in on his father’s last peaceful moments?! The words have conviction, but the speaker of the poem and his intentions are ones coming from selfishness.
Yes, the poem is still about not going down without a fight, but consider the person saying it: for their own gain.
Now if you rewatch the movie, you will see only two characters speak the poem, Dr. Brand (Michael Cain) and Dr. Mann (Matt Damon). Oh, what’s that? The two most selfish characters in the entire movie... and so the plot thickens!
