Just below the text there was a Google ad inviting me to take a quiz. "Christian? Jewish? Muslim? Atheist? See which Religion is Right for You."

Aside from the eccentricity of listing atheism as a religion, I couldn't help wondering what my grandparents would make of this religious matching service. For that matter, what would they make of the idea that you could choose your religion at all? To them, religion was part of your identity, if not your DNA. You were born into it, grew up in it, and died with its prayers.

I noticed this ad because it was attached to the story of a new report on religion in America released by the Pew Forum on Religion and Public Life. The researchers interviewed 35,000 Americans. Their figures show that Protestants now comprise a bare majority — 51 percent — of the population, and that the fastest growing group is the 16 percent now self-described as "unaffiliated."

But what is most fascinating is that 44 percent of Americans have left the religious traditions in which they grew up. They left the religion of their parents with the frequency that they left their old neighborhood.

In my grandparents' day, Americans were divided between the big three religions, sort of like TV networks: Catholic, Protestant and Jew. Now they have fragmented across a spectrum more like cable TV with satellite radio thrown in. The researchers describe a "vibrant marketplace where individuals pick and choose religions that meet their needs." They surf their options.

"We are shopping for everything else, why wouldn't we shop for religion?" asks religion professor Donald Miller of the University of Southern California. Pew's John Green adds, "It's not surprising that we have a marketplace in religious or spiritual ideas." What's qualitatively different these days, he says, is that we have much more religious diversity. "We have more places to move from and more places to move to."

I realize that for many Americans the idea of shopping for eternal truths is still jarring. Even contradictory. The movement from one "tradition" to another may even suggest a kind of promiscuity — a faithless pursuit of faith.

Yet the idea of religion as a personal choice seems thoroughly American — as American as religious tolerance. And increasingly these two ideas may be related.

America has long been regarded as the most religious of Western nations. Six in 10 of us say that religion plays a very important role in our lives. Polls tell us that Americans are more willing to vote for a woman, a black, a Jew than an atheist. Secular Europeans who look at those figures regard Americans as unthinking believers, conservatives following orders delivered from the pulpit.

At home, the culture wars are often polarized between the religious right and the secular left. Leaders of both sides often characterize — perhaps caricature — religious members as people rooted in old ways and immutable ideas. But a huge number of Americans are mobile in pursuit of the immutable.

"We are, as a country, people who want to choose their own identity in a lot of areas of life and religion is one more part of it," says Alan Wolfe of Boston College. There's a difference between an identity that's achieved rather than ascribed. Those who leave their childhood religions largely regard themselves as making their own individual choice. In this cultural context, even staying becomes an active decision.

When religion was cast in stone, it seems to me that we were more likely to cast stones. It may be the new pluralism and the framing of religion as a choice that makes us more accepting.

"You are the artist of your own life when it comes to religion," says Miller. "This enables people to be more thoughtful about what they perceive to be true and right rather than inheriting what passes down to them."

Indeed, if we've left our childhood traditions, if our children may leave ours, there is good reason to nurture what Wolfe calls "intolerance insurance." The Pew study also shows that 40 percent of all marriages are of mixed religious traditions — including "none of the above." We take coexistence pretty literally.

I don't think Americans are just shopping for their beliefs in a trivial sense, trying on creeds like this year's vestment, searching for the latest spiritual fashion. But we are a people on the move. About 40 million of us move to another home every year. So too, we drop in and out of church, U-Hauling our beliefs off in search of a better fit.

Today, we may shop in a spiritual mall. But what good fortune to find the mall paved over the old religious battlefields.

Ellen Goodman is a columnist for The Boston Globe. Reach her at ellengoodman@globe.com.