I recently watched Christopher Nolan's Oppenheimer and found Albert Einstein's character intriguing, especially in his interactions with J. Robert Oppenheimer.
Can anyone explain what was the overall purpose of Einstein's character in the movie, considering he primarily contributed just a few critical dialogues?
It is more than just a few critical dialogues.
Although, Oppenheimer and Einstein disagreed on many things, but he still sought Einstein's advice on nuclear chain reaction and whether it would result in a chain reaction that would destroy the world or not, even though it turned out not exactly right later.
From Screenrant,
Oppenheimer also seeks Einstein's advice once again midway through the movie when he believes that the atomic bomb could set fire to the atmosphere and destroy the whole world. Oppenheimer hands Einstein a piece of paper that explains the scientific theory, to which Einstein responds by telling Oppenheimer to stop working on the bomb. The German physicist also tells Oppenheimer to inform the Nazis about it so they don't make the same mistake. The theory turned out to not be correct, but it goes to show how decisive Einstein was in these tough choices as opposed to Oppenheimer, who was always conflicted.
Besides this, Strauss feels humiliated when Einstein ignores him and thinks it is because of the conversation Oppenheimer and Einstein had by the lake. This made him feel humiliated which later became one of the reasons behind his animosity with Oppenheimer.
From the same article,
Although Einstein's screen time looks limited compared to Oppenheimer three hours run time, he's still one of the most important characters. Ironically, a conversation between Oppenheimer and Einstein that isn't heard until the very last scene is the catalyst for most of the movie. Even though Oppenheimer and Einstein didn't always agree, Oppenheimer often sought Einstein's advice, which is exactly what the German physicist provides in the film. Lewis Strauss (Robert Downey Jr.) feels humiliated when Einstein ignores him, and the AEC chairman believes it's a result of what Oppenheimer told Einstein during their conversation at the lake. This adds to Strauss' animosity toward Oppenheimer and leads to Oppenheimer's hearing.
