Peter Klarnet, a senior specialist in American manuscripts at Christie’s, said that one of the great growth areas in book and manuscript collecting has been science. He said the most valuable Einstein letter was a typed copy of his 1939 note to President Franklin D. Roosevelt, sold at Christie’s for $2.1 million in 2002, that warned of the possibility “of the construction of extremely powerful bombs.” That letter served as a catalyst for research that led to the Manhattan Project.

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The God letter, written the year before Einstein’s death, seems to outline Einstein’s view of formal religion and the idea of a God who plays an active part in everyday life, answering individual prayers. “He did not believe in a God who went around choosing favorite sports teams or people,” Mr. Isaacson said.

But at other times Einstein described himself as “not an atheist,” and the letter does not annul the seemingly spiritual characteristics of his thinking.

“Einstein often uses the word God — ‘God does not play dice with the universe,’” Rebecca Newberger Goldstein, who teaches philosophy and wrote “Plato at the Googleplex: Why Philosophy Won’t Go Away,” said in an interview. “A lot of physicists do this. It misleads people into thinking they’re theists, they believe in God. It’s a metaphorical way of talking about absolute truth. Einstein used it metaphorically and playfully.”

She said he had been religious when he was a child but “lost his religion and science took over.”

“Every time he was asked if he believe in God, he answered cagily: ‘I believe in Spinoza’s god,’” she said, referring to Baruch Spinoza, a 17th-century Dutch thinker who drew from Jewish religion and history. “If you say ‘I believe in Spinoza’s god,’ that’s already saying you don’t believe in what most people believe who believe in God believe. You believe the laws of nature are complete in themselves and contain all the answers.”

Gutkind had made the case in his book that “the Jewish soul is perfect intellectually as well as spiritually,” according to a review in Commentary magazine. “The mathematicized Einsteinian universe is Jewish as well as progressive, because it is anti-mythological.” Commentary also noted Gutkind’s “eagerness to find salvation for modern man in the Jewish spirit” (although the reviewer added that doing so induced Gutkind “to make the most extravagant claims in its behalf”).