“Pope Francis and the Art of Joy,” written by Timothy Egan, appears in The New York Times.

In the modern era, Europe has never had fewer practicing Christians. The United States, according to a Pew survey released this week, is trending in the same direction, led by millennials wary of pontifical certainty.

So why is Pope Francis smiling? For that matter, how did a 78-year-old man with only one working lung become perhaps the most radiant, powerful and humane figure on the global stage? It’s a paradox, but as much of the world has become less identified with organized religion, the leader of the most organized of religions is more popular than ever.

Whether he’s cleaning the feet of the homeless, dialing up strangers for late-night chats or convincing a self-described atheist like Raúl Castro to give a second look at the Catholic church, the pope who took the name of a nature-loving pauper is a transformative gust.

In advance of his visit to the United States later this year, Francis has a chance to move hearts and minds on a couple of intractable issues. He’s called out climate change skeptics and will soon unveil a major encyclical on the environment. Think about that: The church that put Galileo under house arrest for promoting sound science is now challenging the science deniers in power.

This puts him directly at odds with the Republican leadership, and the Koch brothers, who have funded a group that recently accused Pope Francis of “being misled by ‘experts’ at the United Nations.” Speaker John A. Boehner may find that he’s getting more than he bargained for, inviting the pope to become the first pontiff to speak before a joint session of Congress in September.

Francis’s predecessor, while a cardinal, once signed a letter saying homosexuality was “an objective disorder.” This pope would rather focus on the millions of poor clinging to a thin lifeline than talk about people’s sex lives. He speaks truth to power on Armenian genocide, on a Palestinian state, on the Islamic nihilists who behead people of other faiths.

But for all of that, something else explains why the world is so enamored of this pope. Long after we’ve forgotten what his position is on Catholic doctrine, we will remember the serenity of Pope Francis — his self-deprecating lightness of being.  Read more at The New York Times, Opinions.