Albert Einstein used to mention God more frequently than you might expect for a scientist, often in relation to the design of the universe.

Take for instance his opinion on the successful theory of the subatomic world—quantum mechanics. In a letter to physicist Max Born on December 4, 1926, he wrote, “Quantum mechanics is certainly imposing. But an inner voice tells me that this is not yet the real thing. The theory yields much, but it hardly brings us closer to the Old One’s secrets. I, in any case, am convinced that He does not play dice.” Even with the accumulation of a large body of experimental evidence for the validity of quantum mechanics, Einstein continued to repeat this view for the rest of his life.

Or, take his oft-cited pronouncement in 1921 that “The Lord God is subtle, but malicious he is not” (meaning nature may be difficult to decipher, but not bent on trickery). Einstein even wondered whether there was any choice in the cosmic blueprint: “What really interests me is whether God could have created the world any differently; in other words, whether the requirement of logical simplicity admits a margin of freedom.”

But what did Einstein really mean when referring to “God”? And what was his attitude toward religion in general? Recently, the auction house Christie’s announced it was putting one of Einstein’s letters on sale. The fact that in this particular letter Einstein expresses his views on a few of these intriguing questions has helped put the subject of “Einstein’s God” at center stage. And by examining these writings, we can learn quite a lot about the great man’s thinking—not just about religion but science as well.

Einstein wrote the letter up for auction about a year before his death in 1955, and it was addressed to the German Jewish philosopher Eric Gutkind in response to Gutkind’s book Choose Life: The Biblical Call to Revolt, a religious, optimistic, humanistic manifesto based on biblical teachings. The letter is expected to sell for more than $1 million when it goes on sale December 4.

Einstein did not mince words: “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,” he wrote. How can we reconcile these rather harsh statements with the citations about God above? The crucial point to recognize is Einstein does not refer here to God as a cosmic designer. Rather, he expresses his lifelong disbelief in a personal god—one that controls the lives of individuals. In 1929 Rabbi Herbert Goldstein sent him a telegram asking “Do you believe in God?” In response Einstein made an even clearer distinction between the awe humans feel when faced with the vastness, complexity and harmony of nature, and the belief in a god that monitors ethical behavior and punishes the wicked. He admired the Dutch Jewish philosopher Baruch Spinoza, and wrote: “I believe in Spinoza’s god, who reveals Himself in the lawful harmony of the world, not in a god who concerns himself with the fate and the doings of mankind.”

In his letter to Gutkind, Einstein again referred to Spinoza to express his objection to any type of claimed superiority for the Jewish belief in monotheism: “It pains me that you claim a privileged position and try to defend it by two walls of pride—an external one as a human being and an internal one as a Jew. As a human being you claim to a certain extent a dispensation from the causality which you otherwise accept, as a Jew a privileged status for monotheism. But a limited causality is no longer a causality at all [emphasis added], as indeed our wonderful Spinoza originally recognized with absolute clarity.” Einstein emphasized that although he felt “profoundly anchored” in the mentality of the Jewish people, that did not offer him any “different kind of dignity” from all other peoples.

From a historical perspective, it is also interesting to note Einstein differed from some other great scientists in the frequency of his references to God. The great 18th-century French physicist Pierre-Simon Laplace, for instance, never mentioned God in his writings because, in his words, he “did not need to make that hypothesis.” In relation to religious beliefs, on the other hand, even a “heretic” such as Galileo still thought biblical scripture represented truth, if properly reinterpreted when an apparent conflict with scientific evidence arose. On this issue, Einstein’s opinion was entirely different and categorical: “No interpretation [of the Bible], no matter how subtle, can [for me] change anything” about the fact that the text represented to him “an incarnation of primitive superstition.”

To conclude, perhaps the most meaningful sentiment expressed in Einstein’s letter to Gutkind was his agreement with the philosopher on the notion human endeavors should be directed at “an ideal that goes beyond self-interest, with the striving for release from ego-oriented desires, the striving for the improvement and refinement of existence, with an emphasis on the purely human element.” Amen.

Those of us without a million dollars who wish to ponder the letter further can see it on public view in New York City November 30 to December 3.