By Jessica Ravitz, CNN

Decades before atheist scientist and author Richard Dawkins called God a "delusion," one world-renowned physicist - Albert Einstein - was weighing in on faith matters with his own strong words.

“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,” Einstein wrote in German in a 1954 letter that will be auctioned on eBay later this month. "No interpretation no matter how subtle can (for me) change this.”

Dubbed Einstein’s “God Letter” by the Los Angeles-based auction agency that's posting it online, the original document will be up for grabs starting Monday. The opening bid: $3 million.

The letter provides a window into the famed genius's religious beliefs. Einstein wrote it to Jewish philosopher Eric Gutkind, one year before Einstein died, in reaction to Gutkind’s book, “Choose Life: The Biblical Call to Revolt.”

“I’ve been managing high profile auctions since 2005, and this is the most historically significant item to come up ... since I’ve been doing auctions,” said Eric Gazin, president of Auction Cause, the group that's organizing the eBay auction.

Einstein was “one of the most brilliant minds to ever live, but so much of what we know is scientific. … As related to God and Judaism, this is so significant. It really lends itself to further study,” Gazin told CNN. “No one even knew this letter existed till recently.”

But Diana Kormos Buchwald, a history professor at the California Institute of Technology and the director of the Einstein Papers Project, says that's not true.

She said copies of this letter, not to mention numerous additional writings reflecting similar sentiments, have been known to researchers and available for decades, both in the Pasadena-based Einstein Papers Project and The Albert Einstein Archives at Hebrew University in Jerusalem.

The Einstein Papers Project recently published its 13th volume of Einstein’s collected papers.

Einstein, who was raised a secular Jew, was open about his religious views starting in the 1920s, when he became a public figure after winning the 1921 Nobel Prize in Physics, Buchwald said. And biographers, including Walter Isaacson, have documented Einstein’s faith journey.

“There are no revelations here,” Buchwald said of the so-called God letter. “But it is frank in the sense that there are other writings where he says he understands a need for religion and is not derogatory. … Here he makes his own position very clear.”

In the letter about to be offered on eBay, Einstein drove home his strong opposition to the idea that Jews, or any people, may be “chosen.”

Here’s part of what he wrote, according to the Auction Cause translation:

For me the Jewish religion like all other religions is an incarnation of the most childish superstitions. And the Jewish people to whom I gladly belong and with whose mentality I have a deep affinity have no different quality for me than all other people. As far as my experience goes, they are also no better than other human groups … I cannot see anything ‘chosen’ about them.

Buchwald, who has dedicated her life to making Einstein’s works available, believes any discussion of historic documents has value, but she is critical of how this letter is being presented.

There are word choices in the translation that she, as a German speaker, would tweak. She also doesn’t get why it’s said to be written on Princeton University letterhead, when a blown-up image shows it wasn't. Einstein wasn’t even employed there, she pointed out; he was with the Institute for Advanced Study in Princeton, not at Princeton.

Though she views such incongruities as "a bit muddy," she said she wishes the auction agency and seller luck. "It's just hype. ... I don't have a horse in this race."

The letter first became fodder for public discussion and mass fascination when the original sold at a London auction in May 2008 and “poured gasoline on the culture wars between science and religion,” The New York Times reported. Back then, it fetched a mere $404,000. Among the bidders who reportedly lost out that time around: big-name atheist and author Richard Dawkins.

Gazin of Auction Cause, which pairs marketing with charities, said the 2008 anonymous buyer sought his group out for the Einstein letter's sale after noting the agency's other successes. Topping the list: the $2.1 million raked in for an October 2007 letter from Senate Majority Leader Harry Reid, and signed by 41 other Democrat leaders, demanding an apology from Rush Limbaugh.

"More than a few” potential buyers have gotten prequalified to enter this upcoming Einstein letter bidding war, Gazin said. He described those expressing interest so far as people in the technology and atheist communities, as well as university and public museums.

At the current owner’s request, Gazin said, an unspecified portion of the letter's proceeds will go to cancer research.

For those not interested in such heady materials, Auction Cause is offering some less profound items on eBay this month: the dress Maria Menounos wore to the Emmys; shoes from Kourtney Kardashian's closet and time with Howard Stern in the shock-jock's studio.