I was in my early 20s when I first saw Fidelio, Beethoven’s only opera, on stage. I didn’t know that much about it. I knew the rough plot – a woman, Leonore, disguises herself as a man, Fidelio, to get a job as a jailer’s assistant in the hope of finding her political prisoner husband, and she manages to get him freed. I knew it was Beethoven’s response to new thoughts percolating through Europe after the French revolution. And I had heard exactly two of the musical highlights before I went. One is the sublime, slow-burning quartet near the beginning, in which four characters reveal their most heartfelt dreams directly to us, unheard by the other characters. (This may be the most beautiful thing Beethoven ever wrote.) The other is the super-famous Prisoners’ Chorus, in which the men sing powerfully and movingly about our need and right to be free. So I went into the opera that night more than 40 years ago expecting to enjoy myself.

Imagine my surprise to realise this opera has problems!

Before you get mad at me for saying that anything Beethoven wrote has problems, you should know that Beethoven himself was unhappy with the opera. He drastically rewrote it several times over the course of many years, each time tasking a new librettist to fix what the last had written. When the opera originally premiered in 1805 it even had a different name – Leonore, or the Triumph of Conjugal Love. Beethoven ended up writing four Leonore overtures; every time he rewrote the opera he wrote a new one.

Fidelio is full of beautiful music, and beautiful ideas, but it has real dramatic problems. Here are a few:

• The opera is about the noble ideas of love and freedom, but these concepts are more powerfully defined than the characters supposed to embody them. We don’t learn much about who these characters are, except that one is devoted, one is imprisoned for seeking the truth, and that the prisoners all love freedom. There is also, however, a lot of activity that is off these noble topics – a mistaken-identity secondary romance plot that would feel more at home in a comic opera setting, for example.

• The opera is set in a prison, and we are made to feel great empathy for the prisoners. The most famous part of the show is the stirring Prisoners’ Chorus at the end of the first act: We trust in God! We will be free! And then, after they sing this very powerful and moving chorus, the prisoners disappear and we don’t hear from them again until the very last moments of the opera, when they are saved by a totally incredible deus ex machina. What happened to them?

• This scrap of dialogue really bothered me.

LEONORE (to Rocco, the jailer): I often see you coming out of the underground vaults of this castle, almost breathless and exhausted. Why don’t you let me accompany you?

ROCCO: You know I have the strictest orders not to let anyone near the prisoners of the state.

Wait a minute! “Prisoners?” Plural? Even the original libretto for Fidelio implies that, in addition to all the ordinary prisoners we can see, there is a whole dungeon full of other political prisoners. But Beethoven only tells the story of one of them, Leonore’s husband Florestan. Are the other political prisoners saved as well at the end of the opera? Or are they still in the dungeon, down below?

•For me, the most problematic thing is at the very end of the opera, after Florestan is freed. I always want the townspeople to come out and sing about freedom, or tyranny, or justice. A tyrant has been overthrown, after all. Instead, they sing about how great it is for a wife to save her husband. “All who have such a wife, join our song!”

For the past 40 years I have been really bothered thinking about what happened to all those other prisoners. So I decided to make my own version of the piece, to see if I could spend more time with them, to not forget them, to try to place them in the centre of the story.

My new opera, Prisoner of the State, doesn’t use any of Beethoven’s music, but I did want to have it constantly in contact with his libretti. I started by making a kind of skeleton out of the text, filtering out things I felt were off the topic. And I changed the names of the characters into simple descriptions of their jobs: the Assistant, the Jailer, the Governor, the Prisoner.

My process was to simplify the parts of the Beethoven libretti I kept, and to comment on them, by adding new language from other texts. After the Governor orders the Jailer to help him kill the Prisoner, I wrote an aria that is a paraphrase of Machiavelli’s famous dictum that “it is better to be feared than to be loved”. To describe the prison’s structure I added an aria that describes the philosopher Jeremy Bentham’s theory behind the invention of the “modern” prison, modern being 1791, while Rousseau is referenced and quoted in my Prisoners’ Chorus. A section where the guards give their definition of punishment refers to a more recent text by Hannah Arendt.

I was curious who Beethoven thought his prisoners were when he was writing the work in the early years of the 19th century. I found a list from 1805 of crimes for which prisoners from London could be transported to Australia, and I used part of it as a way for the prisoners to introduce themselves to us. “They say I stole a loaf of bread. They say I stole a piece of cloth. They say I stole a lady’s glove …”

And I added the prisoners to almost every scene.

It is probably misguided to try to get your political advice from a piece of art. My project has not been about how to turn Fidelio into a resistance manual. And even though my own country, the United States, has more prisoners than any other, and we are capturing and caging the children of immigrants on our southern border, it really isn’t my intention to make a piece out of current events. Sadly, political prisoners are a timeless lot.

Rather, for me, my new opera goes straight to the heart of classical music. Those of us who love this music tell ourselves there are powerful messages embedded in the work, that this music is capable of ennobling us, of changing lives. It is worth it, occasionally, to ask if our assumptions are true. If they aren’t, shouldn’t we change the things we can to make them true?

Of course, it was Beethoven, with such works as Fidelio and the Ninth Symphony, who pioneered the idea that a composer could challenge society, that music has the power to stand up for something, that a composer’s job might transcend nice tunes and dances and instead take on the meaning of our lives and our obligations to each other. I – and all composers everywhere – inherited that job from Beethoven himself. Maybe that is the best 250th birthday tribute we can give him in 2020.

• David Lang’s Prisoner of the State has its European premiere at the Barbican on 11 January, with Ilan Volkov conducting the BBC Symphony Orchestra.