Christianity has often been used over the centuries to prop up the powerful. But from the beginning, the Christian message has been subversive of political systems, judgmental toward those at the top, and demanding of all who take it seriously.

Pope Francis has surprised the world because he embraces the Christian calling to destabilize and to challenge. As the first leader of the Catholic Church from the Southern Hemisphere, he is especially mindful of the ways in which unregulated capitalism has failed the poor and left them “waiting.”

His apostolic exhortation, “The Joy of the Gospel,” is drawing wide and deserved attention for its denunciation of “trickle-down” economics as a system that “expresses a crude and naive trust in the goodness of those wielding economic power.” It’s a view that “has never been confirmed by the facts” and has created “a globalization of indifference.” Will conservatives among American Catholics who have long championed tax cutting for the wealthy acknowledge the moral conundrum that Francis has put before them?

But American liberals and conservatives alike might be discomfited by the pope’s criticism of “the individualism of our postmodern and globalized era,” since each side defends its own favorite forms of individualism. Francis mourns “a vacuum left by secularist rationalism,” not a phrase that will sit well with all on the left.

And in light of the obsessive shopping on Cyber Monday and Black Friday, here is a pope who paints consumerism in the darkest of hues. “We are thrilled if the market offers us something new to purchase,” he writes. “In the meantime all those lives stunted for lack of opportunity seem a mere spectacle; they fail to move us.”

Yet this critic of our age refuses to be gloomy, scolding “querulous and disillusioned pessimists” whom he labels “sourpusses.” I like a pope who takes a stand against sourpusses.

Francis makes many liberals swoon without, in a conventional sense, being a liberal. He has also split American conservatives between those trying to hold fast to him and those who know that he is, from their perspective, up to something dangerous.

All sides realize where the energy of Francis’ pontificate lies. He’s not the first pope to denounce our unjust economic system. Pope John Paul II regularly decried “imperialistic monopoly” and “luxurious egoism.” Pope Benedict XVI condemned “corruption and illegality” in “the conduct of the economic and political class in rich countries” while speaking approvingly of “the redistribution of wealth.”

The difference is that a concern for the poor and a condemnation of economic injustice are at the very heart of Francis’ mission. “In this system, which tends to devour everything which stands in the way of increased profits,” he writes, “whatever is fragile, like the environment, is defenseless before the interests of a deified market, which become the only rule.” Can you imagine an American liberal who would dare say such things?

Conservative American Catholics have been quick to point out that toward the end of “The Joy of the Gospel,” Francis strongly affirms the church’s opposition to abortion. This is, indeed, one of the ways in which he is not a conventional liberal. He speaks of “unborn children” as “the most defenseless and innocent among us.” He insists that the church’s position is not “ideological, obscurantist and conservative,” but rather is “linked to the defense of each and every other human right.”

Yet almost immediately, he adds that “it is also true that we have done little to adequately accompany women in very difficult situations,” and quickly moves back to his broader stand on behalf of “other weak and defenseless beings who are frequently at the mercy of economic interests or indiscriminate exploitation.”

It’s quite true that liberals who love Francis need to come to terms with aspects of his thought that may be less congenial to their assumptions. But the high priority he has placed on battling economic exploitation, his warnings against those who “remain intransigently faithful to a particular Catholic style from the past,” and his unhappiness with the rise of ultra-orthodoxy -- he upbraids “dour judges bent on rooting out every threat and deviation” -- test conservatives even more.

In light of a recent past in which conservatism was gaining the upper hand in the American Catholic church, progressives have reason to be elated. Conservative Catholics know this. That’s why they are torn between expressing loyalty to a pope who has captured the popular imagination and fretting over whether he is transforming the church with a speed that few thought was possible.