Einstein was not a believer as a recently discovered letter written a year before his death makes clear. Here is what he wrote:
"The word god is for me nothing more than the expression and
product of human weakness, the Bible a collection of honourable,
but still primitive legends which are nevertheless pretty childish.
"No interpretation no matter how subtle can (for me) change this..."
"For me the Jewish religion like all others 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."
Einstein's words in this letter make clear that Einstein was, at least privately, not a believer.
In other writings, he ridiculed the idea of a personal god who answered prayers in much the same language that Sigmund Freud used. When he did say he believed in god, he made it clear that he believed in the universe and its laws as god. This, of course, is identical with atheistic pantheism and was nothing but a dodge. He knew better than to admit he believed in no god. He knew how much it would cost him.
He came to the U.S. as a refugee from deadly religious persecution, after all. Therefore, he was careful to use the g-word on occasion and never speak freely in public about what he thought and believed. As a Jew, Einstein was a member of reviled minority in Europe. In America, he was a foreigner seeking a safe refuge. Whatever his private thoughts might have been, he knew his life would be different if he did not remain popular.
For it's a sad fact, that to become known as an atheist is to find oneself suddenly unpopular and thrust into a position of having to defend yourself or your opinion (indeed, all of your opinions) when you would rather be doing other things. His description of his de-conversion at the age of 12 shows that he understood the powerful forces behind religion. He wrote that the "religious paradise of youth", in which he believed what he was told was crushed. He wrote:
"The consequence was a positively fanatic freethinking coupled
with the impression that youth is being deceived by the state
through lies; it was a crushing impression."
After reading these quotations, one might wonder why Einstein never called himself an atheist, even in private, and why he often criticized atheists and atheism. If one reads his criticisms of atheism, they make it clear that Einstein thought atheism was limited to "strong atheism", which is the idea that atheists are absolutely sure that there is no god. He took to heart the criticism of strong atheism that such atheists were claiming to know with certainty that god did not exist, which of course neither they nor anyone else can claim--anymore than anyone can claim to know for certain that god does exist.
As I mentioned before, this strong atheist position is, I think, a result of the deliberate misuse of solipsism to separate atheists into two groups: Strong atheists and weak atheists/agnostics. The weak atheists/agnostics are those who will admit that they can't possibly know that god doesn't exist for certain. Solipsism is misused to try to convince them that they are actually agnostic. The strong atheists are those who can be goaded into making the affirmative assertion that they are absolutely certain that god doesn't exist, which ordinarily would imply they were assuming a burden of proof--if not "the" burden of proof regarding god's existence.
It is no surprise that Newton was a believer, given the age in which he lived. Newton grew up in the dark ages of science, well before Darwin published "The Origin of Species". Others, such as Richard Dawkins, have said that a person can be excused for being a believer when there was no other explanation for the complexity of the universe and life.
I am not so sure of that because I think it should have been clear after it was proved that the Earth was round that all "god of the gaps" based arguments were logically invalid, but it is certain that it would have been harder to justify being a non-believer before Darwin. And, it just so happens, that it was Newton himself who put the final nail in the coffin of the flat earth gods by showing that not only was the Earth round, but there was a describable, predictable force at work that kept things from falling off the Earth.
More important than the lack of Darwin's influence, Newton was raised and educated in a time when an atheist could not hope to be able to obtain an education, get a teaching position and publish his ideas. I wonder if we would even know Newton's name had this not been true. How many other brilliant men never achieved their potential because they dared to think for themselves on the subject of religion? How many Newtons were expelled from Universities, burned at the stake, ostracized, etc.? We will never know.
“We would be 1,500 years ahead if it hadn't been for the church dragging science back by its coattails and burning our best minds at the stake.” Catherine Fahringer, Interview, San Antonio Express News, Portrait of an Atheist by Craig Phelon, March 24, 1991).
I think Ms. Fahringer's observation is brilliant. When the religious point out that Isaac Newton was a devout christian, this is the right response:
"If it hadn't been for the church persecuting all the best minds, running them out of academia or even killing them, we would never have heard of Isaac Newton. Someone else would have made his discoveries long before he was born. He would have been the crackpot Sunday school teacher he was meant to be."
Or, maybe, he would have been raised without superstition and would still have been an intellectual luminary but wouldn't have been a believer.
In closing, I would like to make a more general observation about the way that Newton's fame actually highlights one of the many ways in which religion can be said to constitute an evil influence.
By hindering education, the religious have prevented and continue to prevent humanity from expanding in the one direction which is both limitless and essential for our survival and well being. Our best economic system, capitalism, is predicated upon expansion. If any capitalist country's economy stops expanding, it's in trouble--especially if it does not limit the growth of its population (and, even if it does, the Earth's human population will continue to grow, leading to the same result by virtue of immigration).
Such expansion using old methods is necessarily finite and it is arguable that we are starting to reach its limits. Soon the Earth will reach the limit of its capacity to absorb the effects of our activities. But, if we could change those activities so that they did not have the same effect on the Earth, we could effectively expand our horizons. Humanity still faces many problems. Our only hope of solving them lies in the limitless potential of the human mind. So long as it remains fettered to the Dark Ages, our prospects will remain dim.