For anyone who doesn't know the entire poem, here it is: Dylan Thomas - Do Not Go Gently Into That Good night.
Movie spoilers ahead
Now for some super hippy analysis of the Poem and its meaning in contect of the film. Please note: this is not an be all-end all summary.
This poem is, at its core, a summary of human triumph and struggle in the darkest hours we face. In terms of the film, the darkest hours are a prelude to the upcoming mission: Travelling light years away, through a wormhole, into the gravitational pull of a black hole.
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 Do not go gentle into that good night.
Professor Brand knows this more than most. He is presented as (possibly) the oldest character in the film. Lived well past his years in terms of the current climate of the Earth, and he is fighting a battle that he cannot win. Not only is he fighting against age, he is also living a lie. A promise that was made to not only his science team, but all of man kind. He is fighting a battle for not just his life, but his sanity.
Good men, the last wave by, crying how bright Their frail deeds might have danced in a green bay, Rage, rage against the dying of the light.
Wild men who caught and sang the sun in flight, And learn, too late, they grieved it on its way, Do not go gentle into that good night.
The next two sections are a perfect summary of Cooper. A man, out of his element, a genius (if you will), an engineer and pilot, now adapting to a world that doesn't need him. He fights every day in his own way, to teach his children; not to just accept what the world has to tell them, back to try and choose their own destiny. He is a wild man; Icarus, reaching for the sun, only to learn that he could never get there. Not without a massive sacrifice.
Grave men, near death, who see with blinding sight Blind eyes could blaze like meteors and be gay, Rage, rage against the dying of the light.
And you, my father, there on the sad height, Curse, bless, me now with your fierce tears, I pray. Do not go gentle into that good night. Rage, rage against the dying of the light.
This section is a bit of foreshadowing. In terms of the movie it makes sense though (seeing as the entire plot is a self fulfilling prophecy). Coopers "Blinding Light" could be seen as the moment he enters the dimension set up by "them". Dr. Mann even predicts this moment in a different way. It certainly would have been a near death experience for Cooper if it was an unaltered black hole that he was falling into. Regardless, Coopers moment... blind eyes could blaze like meteors and be gay (happy). In that time-space, Cooper realizes that he may very well die, but he can still save humanity. He does everything he can, and trusts in the love of his daughter to see the truth. Murph, in this moment, has the love and inspiration, burning bright, that has literally transcended time and space. The love that only a father taken from his family too soon could give.
The last passage, could be in direct relation to both Murph or Cooper (Mostly Murph though). She has solved the problem of gravity, effectively saving mankind. But thanks to relativity, you have to assume that she knows she won't see her dad again for a long time. Even though for him, it's not a great deal of time... but for Murph, he has been alone for 40-50-60 years. The line says Curse, bless, me now with your fierce tears. To me this is a beautiful line. She can be both cursing him because he left her when she was so young. Not fully understanding the reasons why. But at the same time she blesses him, because of his sacrifice, mankind is saved. The old argument, "Would you kill 1 baby to save a thousand" comes to mind. Of course, Cooper didn't kill anyone, but he effectively gave up his children (and grandchildren) for a chance to save man kind.
The cursing and blessing is a hint at the futility of struggle (everyone dies), but the human drive to postpone it. You can almost hear this last line of the poem being read by Murph, almost like a bedtime prayer to her "ghost". Do not go gentle into that good night... 8 of the most powerful words in the film. These 8 words sum up all of human existence. We do not go gentle into that good night. We try. We struggle. We break the bonds of oppression and seek new boundaries. We Rage. Sometimes against each other. Some times against unrelated things. But always, in the pursuit of something bigger. Something grander than ourselves. In my experience, the very heart of human kind wants to explore. This poem, and this film, are a beautiful example of why we should be out there looking for something bigger. Not because there's a profit in it. Not because it could be fun. Not because we'd get famous doing it. But because human nature calls for us to be wild. And at the end of the day, nobody wants to go gently into that good night.