Pope Francis didn't make global headlines on Aug. 14, 2014, when -- with permission from Communist Party leaders -- Shepherd One flew through Chinese airspace on the way to Seoul, South Korea.

Still, it was a symbolic moment that hinted at progress, after decades of bitter persecution for Chinese Catholics loyal to the Vatican. Then, a year later, Bishop Zhang Yinlin was ordained as bishop of Anyang, after nods of approval from both Rome and Beijing.

So things are looking up for religious freedom in China?

If so, what did it mean when the Rev. Gu Yuese -- leader of the largest Protestant megachurch in China's state-approved Three-Self Patriotic Movement -- was recently jailed after opposing the government's demolition of thousands of crosses in "China's Jerusalem," part of Zhejiang province.

"There may be all kinds of reasons they arrested him, other than that he is famous and his church is huge. It's hard to know what's happening, when you're talking about the Chinese government," said Rodney Stark, co-director of the Institute for Studies of Religion at Baylor University. He is the author or co-author of 36 books on various religious issues, past and present, including "A Star in the East: The Rise of Christianity in China," with sociologist Xiuhua Wang.

"We can say that we haven't seen the Nero effect yet, with the government putting heat on Christians because China's economic numbers are looking bad. … Also, it's important to remember that we've reached the point where many leaders in China now have kids who are Christians. In some villages, you may have a Communist Party leader with a cross on his wall."

The bottom line: There is truth in the popular saying that China is so huge and complex that just about anything someone says about religion in China will be true -- somewhere in China.

At the same time, it's crucial to understand that human-rights trends among the 1.38 billion people in China, even among minority groups, will have a major impact on world affairs. When contemplating the future, it's especially important to note that Christianity is growing rapidly in China's leadership class in economics, academia, technology and even government, said Stark.

In "A Star in the East," Stark and Wang note that "tens of millions of Chinese have embraced Christianity -- thousands more convert every day and more than 40 new churches open every week (not counting new underground congregations). If this trend were to hold for another decade, there would be more Christians in China than in any other national in the world."

At the center of this drama are often-conflicting estimates of how many Christians there are in China. Some experts put that number as low as 16 million, while others claim it's as high as 200 million.

Stark has argued that researchers should focus on a 2007 survey by Horizon Ltd., built on thousands of face-to-face interviews conducted by "China's largest and most respected polling firm." However, he noted that 62 percent of self-professed Christians declined to be interviewed in that study. Also, some Chinese will say they believe in Jesus, while denying they are Christians since they are not part of a formal Christian institution. Is a home Bible study a "church"? Not for millions of Chinese believers.

Taking these factors into account, Stark and Wang have, using the 2007 study, offered a conservative estimate that China contained 60 million Christians at that time. Comparing that number with earlier surveys, they believe Christianity had been growing at the rate of 7 percent a year in the quarter century preceding the 2007 study.

If that estimate is solid, then the number of Christians in China would have reached nearly 100 million in 2014 -- with projected growth to nearly 150 million in 2020 and about 580 million by 2040.

Much of that growth will remain hard to document since it will happen in thousands of "underground" -- meaning unregistered -- Protestant and Catholic congregations.

"Of course, in some parts of China you have underground churches, quote-unquote, that are four or five or six stories tall," said Stark. "That's a pretty strange kind of underground. That's pretty overt. …

"Then again, all of this could change tomorrow, because that's the kind of government you're dealing with in China."