The letter, estimated to fetch between $1 and $1.5 million , surpassed expectations at Tuesday's auction at Christie's in New York. The "remarkably candid, private letter was written a year before Einstein's death and remains the most fully articulated expression of his religious and philosophical views," according to a statement about the letter on Christie's website.

Nobel prize-winning physicist Albert Einstein thought about more than just the theory of relativity or gravitational waves . In fact, a letter he wrote in 1954, in which he discussed his inner-most thoughts about God and religion, just sold for $2,892,500 .

This undated photo provided by Christie's shows the first page of Albert Einstein's "God Letter," dated January 3, 1954.in which he offers his candid and unvarnished opinion that: "The word God is for me nothing but the expression and product of human weaknesses, the Bible a collection of venerable but still rather primitive legends." It is being auctioned by Christie's on Dec. 4, 2018.

While Einstein is not widely known for his discussion of religion, the then-75-year-old was moved to write what Christie's calls a "direct" and "unvarnished" letter on the topic after reading a book by Jewish philosopher, Eric Gutkind. Gutkind's book "Choose Life: The Biblical Call to Revolt" had garnered a small following at the time.

Although he identified as Jewish, Einstein did not agree with Gutkind about the role of God in an individual's life and a person's free will. In the letter, Einstein complained that Gutkind's book was "written in a language which is inaccessible to me."

The letter reads: "The word God is for me nothing more than the expression and product of human weaknesses, the Bible a collection of honorable but still primitive legends. No interpretation, no matter how subtle, can (for me) change anything about this."

(See the full translation of the letter here)

Once made public, the "God letter" became Einstein's single most famous letter on the subject of God, his Jewish identity and man's eternal search for meaning, according to Christie's. The letter was previously sold for $404,000 when it surfaced in 2008 and was again auctioned on eBay with a starting price of $3 million in 2012 (though it appears to have not been sold at that time). It's also just one of several artifacts of Einstein's have been sold over the past year.

Despite Einstein's critique of Gutkind's religious and philosophical approach, he noted the two shared common views when describing what people strive for in life: "an ideal that goes beyond self-interest" and a "release from ego-oriented desires," among other things.

Ultimately, Einstein said he'd be able to put his differences aside, reflecting the scientist's rational nature, which many grew to respect.

"What divides us is only intellectual padding," he wrote.

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