To understand Pope Francis -- his purpose, his program and its potential pitfalls -- it's useful to think about what's been happening to New York City's Jews.
From the 1950s on, New York's Jewish population declined, amid suburbanization and assimilation. But over the last 10 years, the numbers began to rise again, climbing 10 percent between 2002 and 2011.
But this growth was almost all among Orthodox Jews. The city's Reform and Conservative populations continued to drop, as did Jewish religious observance overall.
As a result, New York's Jewish community is increasingly polarized, with more Jews at the most traditional end of the theological spectrum, more Jews entirely detached from the institutions of their ancestral faith -- and ever-fewer observant Jews anywhere in the middle. What's happened in New York is happening nationally: A recent Pew study found a similar pattern of growth among the Orthodox and a similar waning of religious practice and affiliation in the rest of the American Jewish population.
This is not just a Jewish story. It's been the story of religion in the West for over 40 years. The most traditional groups have been relatively resilient. The more liberal, modernizing bodies have lost membership, money, morale. And the culture as a whole has become steadily more disengaged from organized faith. There is still a religious middle today, but it isn't institutionally Judeo-Christian in the way it was in 1945. Instead, it's defined by nondenominational ministries, "spiritual but not religious" pieties and ancient heresies reinvented as self-help.
Of late, this process of polarization has carried an air of inevitability. You can hew to a traditional faith in late modernity, it has seemed, only to the extent that you separate yourself from the American and Western mainstream. There is no middle ground, no center that holds for long, and the attempt to find one quickly leads to accommodation, drift and dissolution.
And this is where Pope Francis comes in, because so much of the excitement around his pontificate is a response to his obvious desire to reject these alternatives -- self-segregation or surrender -- in favor of an almost-frantic engagement with the lapsed-Catholic, post-Catholic and non-Catholic world.
The idea of such engagement -- of a "new evangelization," a "new springtime" for Christianity -- is hardly a novel one for the Vatican. But Francis' style and substance are pitched much more aggressively to a world that often tuned out his predecessors. His deliberate demystification of the papacy, his digressive interviews with outlets secular and religious, his calls for experimentation within the church and his softer tone on the issues -- abortion, gay marriage -- where traditional religion and the culture are in sharpest conflict: These are not doctrinal changes, but they are clear strategic shifts.
John Allen Jr., one of the keenest observers of the Vatican, has called Francis a "pope for the Catholic middle," positioned somewhere between the church's rigorists and the progressives who pine to Episcopalianize the faith.
But the significance of this positioning goes beyond Catholicism. In words and gestures, Francis seems to be determined to recreate, or regain, the kind of center that has failed to hold in every major Western faith.
So far, he has at least gained the world's attention. The question is whether that attention will translate into real interest in the pope's underlying religious message or whether the culture will simply claim him for its own -- finally, a pope who doesn't harsh our buzz! -- without being inspired to actually consider Christianity anew.
In the uncertain reaction to Francis from many conservative Catholics, you can see the fear that the second possibility is more likely. Their anxiety is not that the new pope is about to radically change church teaching, since part of being a conservative Catholic is believing that such a change can't happen. Rather, they fear that the center he's trying to seize will crumble beneath him, because the chasm between the culture and orthodox faith is simply too immense.
And they worry as well that we have seen something like his strategy attempted before, when the church's 1970s-era emphasis on social justice, liturgical improvisation and casual-cool style had disappointing results: not a rich engagement with modern culture but a surrender to that culture's "Me Decade" manifestations -- producing tacky liturgy, ugly churches, Jonathan Livingston Seagull theology and ultimately empty pews.
Francis seems acquainted with that danger - witness his warnings against a church that just "becomes an NGO," or against reducing Christianity to "taking a spiritual bath in the cosmos."
But the test of his approach will ultimately be a practical one. Will the church grow or stagnate under his leadership? Will his style just win casual admirers, or will it gain converts, inspire vocations, create saints? Will it actually change the world, or just give the worldly another excuse to close their ears to the church's moral message?
By his fruits we will know - but not for some time yet.
Ross Douthat is a columnist for The New York Times.