Shortly before the start of World War II, Albert Einstein, perhaps the world's most famous theoretical physicist, wrote a letter to a colleague detailing his thoughts on the "power of the resistance" of the Jewish people. And now that letter is set to go up for auction and it could fetch a staggering sum.

The letter, postmarked June 10, 1939, and sent to E.J. Brown of the Arnold Constable & Co. department store, congratulates Brown for the work he did for refugees during Dedication Week.

"The power of resistance which has enabled the Jewish people to survive for thousands of years has been based to a large extent on traditions of mutual helpfulness," Einstein wrote in letter. "In these years of affliction our readiness to help one another is being put to an especially severe test. May we stand this test as well as did our fathers before us."

SHOCKING EINSTEIN LETTERS, REVEALING 'HITLER-INSANITY,' UP FOR AUCTION

He continued: "We have no other means of self-defense than our solidarity and our knowledge that the cause for which we are suffering is a momentous and sacred cause."

“Dedication Week” was a campaign to raise public consciousness regarding the need for Jewish rescue. Less than two weeks before sending this letter, Einstein gave the official dedication speech for the Jewish Palestine Pavilion at the New York World’s Fair to a crowd of 100,000 visitors.

The letter is set to be auctioned by Nate D. Sanders and has a starting price of $20,000.

Einstein had written similar letters attesting to the "power of resistance" of the Jewish people, including one he wrote two days later.

"The power of resistance which has enabled the Jewish people to survive for thousands of years has been based to a large extent on traditions of mutual helpfulness," Einstein wrote in the June 12 letter. "In these years of affliction our readiness to help one another is being put to an especially severe test. May we stand this test as well as did our fathers before us."

That letter, sent to Dr. Maurice Lenz, sold for $134,344, the auction house added.

RARE EINSTEIN LETTERS, REVEALING HIS ESCAPE FROM THE NAZIS, UP FOR AUCTION

In recent months, Einstein's letters have garnered significant interest at auction. In March, along with the June 12, 1939 letter, two other letters went up for auction, including one which he detailed his thoughts on "Hitler insanity."

In December, a letter in which he discussed his Jewish faith as well as "man's eternal search for meaning" sold for a record-breaking $2.89 million.

In October 2017, Einstein's note on the theory of happiness sold to an unknown buyer at a Jerusalem auction for $1.56 million.

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Fox News' Sasha Savitsky contributed to this story.