Chicago – A letter from Albert Einstein to a Chicago man thanking him for helping Jews to escape Nazi Germany has been made public by his daughter.

Enid Bronstein has kept the letter penned by Einstein in a safe deposit box for the last 50 years, she told Chicago’s WGN TV.

The letter was written to David Finck, a New York financier who helped fund the emigration of Jewish refugees from Europe in 1939 before the outbreak of World War II.

“May I offer my sincere congratulations to you on the splendid work you have undertaken on behalf of the refugees,” Einstein said in the letter written in June 1939. It is one of three such letters known to be written by Einstein, himself a Jewish refugee from Nazi Germany.

“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. 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,” the letter also said.

Bronstein said she guarded the letter carefully after he died 50 years go. “I wanted to keep the letter to show it to my children and grandchildren so that they would get the message that every contribution, no matter how small, is important,” she told WGN.

She said she will donate it to the U.S. Holocaust Memorial Museum in Washington DC. She could have sold it for thousands of dollars.