The Divan Orchestra, Mr. Barenboim said, was not created as a political orchestra, or as an orchestra for peace, but simply as a way to promote dialogue — starting with its own members.

“I sat them together, so you had a Syrian cellist and an Israeli on the same stand,” Mr. Barenboim said. “What do they do? First of all, they tune to the same A. So they have to listen. Then they try to play the same way, with the same bow strokes. They do that for six hours a day, and then they eat in the same dining room. Their attitude changes.”

“I always say to them: ‘I expect all of you to agree on how to play Beethoven,’” he said. “I don’t expect you to agree on the other side’s narrative. But I do expect you to try to understand it and respect it.”

Making music is hard work: Mr. Barenboim, who led the rehearsals this week in English — dipping into German, Spanish or French where appropriate — could be a demanding taskmaster. But he was also quick to show warmth and delight, and to offer guidance.

“Wonderful. Wonderful!” he said after a run-through, once they had earned it.

During rehearsals, the players — the youngest are in their teens, the oldest in their 40s — applauded one another and exchanged sympathetic looks after Mr. Barenboim’s criticisms.