But he also affirms that religion will never disappear and that the "New Atheists" don't have the answers to meeting human needs.
In his 31 years, Epstein seems to have done most everything, from being a singer and composer in a professional rock band to studying ancient Aramaic literature at Jerusalem's Hebrew University.
During a lengthy phone conversation, he previewed some of the points he will raise when he speaks at Rosh Hashanah services at Adat Chaverim, the local Congregation for Humanistic Judaism, points that he analyzes more deeply in his forthcoming book, "Good Without God."
Humanistic Jews do not believe in an omnipotent supernatural power, "but in this day and age, the term God can mean anything you want it to be," he said.
"If you mean a bearded deity on a throne who worries about your personal lifestyle and issued 613 commandments, we reject that. But if your god stands for nature, or the universe, or love, that's fine," he added.
"The real point is that this is the only world we can ever know and that this life is the only chance we get to make a difference."
Epstein also thinks that the oft-repeated injunction to repair the world misses the mark, because it assumes there once was a perfect world, which degenerated and must now be fixed.
"I prefer the phrase 'bniyat olam,' to build the world," Epstein said. "Humanistic Judaism teaches that there never was a utopia, but this lack of perfection is no excuse for intellectual or spiritual laziness.
"We must build our relationship to our fellow humans and the world brick by brick, for we are responsible for one another and no one else will do the work." He added facetiously, "The most pernicious rhyme in our language is 'Humpty Dumpty,' the idea that there was once a perfect white egg which shattered into a million pieces, and no one could put it together again."
Many, but not all, Humanists are atheists or agnostics, but Epstein is no fan of such popular proponents of the "New Atheism" as writers Richard Dawkins, Sam Harris or Christopher Hitchens.
In an early story about these writers in Wired Magazine, the cover proclaimed "No heaven, no hell -- just science."
That distillation oversimplified a "painfully complex" question, Epstein said. "Science is the best tool for determining the truth about us, but that is not the same as doing something about it. It is not enough to just observe, we must engage in our community and do something."
Epstein also distinguishes his philosophy from that of Jewish, mostly Yiddish-speaking, secularists of previous generations, who maintained that religion would ultimately disappear as mankind became increasingly rational.
"Religion is not primarily about faith in God; it is about community, identity, heritage and being of service to others," he said. "We Humanists must also do more to meet these needs, rather than complain about what others believe.
"As a friend pointed out to me, when Martin Luther King Jr. gave his most famous speech, he did not say, 'I have a list of complaints,' but 'I have a dream.'"
Questioned about the role of religion in the current presidential race, Epstein recalled that slamming the other candidate's religion or piety has a long, dishonorable tradition in American politics.
In the election of 1800, when Thomas Jefferson challenged incumbent John Adams, the Federalist Alexander Hamilton, an Adams partisan, swiftboated Jefferson in the following advertisement.
"The Grand Question Stated: At the present solemn and momentous epoch, the only question to be asked by every American, laying his hand on his heart, is 'Shall I continue in allegiance to GOD _ AND A RELIGIOUS PRESIDENT; or impiously declare for Jefferson - and no god!!!"
Epstein was born in the Flushing section of Queens, N.Y., then a widely diverse, multiracial community, and he had his bar mitzvah in a local Reform synagogue.
"It seemed to me then that no one took the message of religion seriously, and everyone recited prayers just by rote," he said. "So I soon started exploring everything except Judaism and visiting every place except Israel."
After graduating from the University of Michigan, Epstein studied Buddhism in Taiwan and China, then joined the rock band Sugar Pill and recorded two albums. Like many of his contemporaries, Epstein said, "I wanted to express myself through art and music, rather than religion."
At this point, Epstein discovered the pioneer Humanistic Judaism congregation established by Rabbi Sherwin Wine in suburban Detroit, and "I finally connected to my heritage, but also realized that I had a lifetime of learning ahead of me."
The process began with five years of study in suburban Detroit and Jerusalem at the International Institute for Secular Humanistic Judaism, followed by a master's degree in Judaic studies at the University of Michigan, and another master's degree in theology and comparative religion from the Harvard Divinity School.
Four years ago, he became a chaplain at Harvard, where he advises students in the Secular Society, Interfaith Council and the Harvard Humanist Graduate Community.
Epstein's thoughts are frequently expressed in national publications and on radio networks, and he is one of a select group of invited panelists for the On Faith blog, started jointly by Newsweek and the Washington Post.
According to the 2000 National Jewish Population Survey, there are 1.6 million American adults and children who define themselves as "just Jewish," and who are either secular or without any denominational affiliation.
Epstein said that one out of five young American Jews between ages 18 and 25 fall into that category, and that globally 1.1 billion human souls do without formal religion.
If all secular and unaffiliated American Jews joined together, they would form the country's second largest Jewish denomination, barely trailing Reform membership.
The problem for Epstein and other Humanist leaders is that the 1.6 million are not organized and are not joining the existing congregations/communities of the Society of Humanistic Judaism.
After more than 40 years on the North American scene, the movement claims only some 10,000 adherents and 30 congregations, according to national executive director M. Bonnie Cousens.
Only six of the congregations are led by ordained rabbis, the others by lay leaders or "madrichim."
What accounts for the low figures, given the large pool of potential members?
There are no clear-cut answers, but Cousens and other national leaders speculate that secular Jews, having arrived at this state through personal doubts and mental wrestling, are just not prone to join any organization.
Another cause may be that there is still, at times, an onus attached to "coming out" as a secular or atheistic Jews, though reactions by more traditional Jews seem less shocked and outraged than in the past.
Rabbi Miriam Jerris, president of the Association of Humanistic Rabbis, bemoaned the society's lack of popular visibility, saying, "There are so many Jews out there just waiting to discover us."
Epstein is more upbeat. Drawing on his four-year experience at Harvard, he said that in the beginning only four students regularly attended his meetings.
Now his meeting rooms are crowded and last year, when he organized an international conference on "The New Humanism," some 1,100 people attended.
"We may be a small minority, but minority groups can have a profound impact on mass movements," he said. "Even now, I believe, liberal mainstream congregations are speaking more to human needs than divine needs."
To have a growing impact, Humanistic Jews "must sing and must build, and I mean that literally and metaphorically," he said.
So Epstein is hopeful, but within reason. Quoting playwright Tony Kushner, Epstein said, "We are optimists, but we are not stupid optimists."