Ben Foster in “The Survivor.” Photo: Leo Pinter/HBO.

Acting isn’t easy, especially when you are a cantor with no acting experience. Having to lose 25 pounds doesn’t help, and being in a movie with heavy hitters like Ben Foster and Danny DeVito can add some pressure.

So it was for cantor Erik Contzius, who has a small but meaningful role in “The Survivor,” airing now on HBO Max.

The film stars Ben Foster as Harry Haft, who the Nazi forced to box other Jews in Auschwitz; the winner would get extra food and the loser was killed. It’s based on a book by Haft’s son,

How did Contzius get the role where he sings a soulful “Avinu Malkeinu?”

In 1998, he recorded the song. Decades later, famed director Barry Levinson was on Spotify, and heard the digital version and felt it would be perfect.

In 2018, Contzius got a call to see if he was available to shoot a scene for the movie. And he was.

“I was nervous, but I got over my nerves after the first day of shooting,” Contzius said.

To slim down, the cantor drank weight-loss shakes, excluded carbs, and consumed 800 calories a day.

“Losing the first 10 was easy, but the rest was hard,” he said.

Contzius said Foster stayed in character on set, maintaining a Polish Jewish accent, and asking him about the different shakes.

After getting cantorial ordination from Hebrew Union College, Contzius was a pulpit cantor at Temple Israel in Omaha, Nebraska; Knesseth Israel in Elkins Park, Pennsylvania; and Temple Israel in New Rochelle, New York.

“We never know the opportunities we will get in life, and this was a great one. It was such an honor. The director, the cast, and really everyone was so respectful and kind, so it was a great and unforgettable experience,” he said.

Hailing from New Jersey, the 53-year-old said the role meant a lot to him, and that the movie will be extremely impactful on the public. He added that it’s surreal that his name is on the soundtrack along with Hans Zimmer, one of the most famous film composers of all-time.

The interim cantor at Temple Tikvah in New York, said the film is a juggernaut.

“It’s not only a Holocaust movie, it’s also a boxing movie, it’s a love, story, but at the heart of it, it’s about the power of the human spirit and about perseverance in the face of seemingly insurmountable obstacles.”

The film is produced by Matti Leshem, founder of New Mandate Films, as well as Bron Studios. In an e-mail ahead of the screening at Yad Vashem in Israel, Leshem explained why this film  is so personal.

“My father survived the Holocaust living under an assumed identity and forging identity papers for the Czech resistance,” Leshem wrote. “My grandmother was murdered in Auschwitz and my aunt died in the ghetto in Terezin. So, I have lived with the specter of this reality my whole life. When I read the script, I knew that telling the spectacular story of Harry Haft was going to be something I simply had to do. … I feel strongly that we must keep telling these incredible stories of the Holocaust because if we don’t, especially in these times as we have seen, we are vulnerable to the idea that it didn’t happen.”

The author is a writer based in New York.