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.