There are arguably a number of explanations as to why Christianity grew so dramatically in China despite the dogged efforts of the Communist Party to control and even eliminate Christianity--and other religions--in China. Ironically, the growth of Christianity in China may be partially due to the Communist government's own efforts to weaken the Christian church. Soon after taking power, the Chinese Communists began expelling foreign missionaries from the country and forcing Chinese believers to cut their ties with their co-religionists in the West. The idea was to cut off Chinese Christians from any outside support. However, forcing Chinese believers to cut their ties with foreigners may have actually helped the Church in a way, by undermining the idea that Christianity was merely a "foreign religion" (however, to be fair, Catholics were more adversely affected than Protestants by these efforts to cut off believers from the outside world, given that the head of the Catholic church, the Pope, was a foreigner). Moreover, while the government's persecution of Christians may have caused some nominal Christians to abandon their professed faith, it seemed to strengthen the faith of the truly committed, and it may be that the faith of these committed Christians helped attract converts. Furthermore, in more recent years, widespread disillusionment with Communist ideology has led quite a number of Chinese to look for something else to believe in, and many of them have chosen Christianity. Of course, most important, I would argue, was the work of the Holy Spirit, moving in the hearts of so many Chinese people.
Nevertheless, lest I be accused of engaging in triumphalism, it should be acknowledged that the Church in China continues to face many challenges. The Chinese government remains hostile towards Christianity and has not ceased its efforts to limit or even prevent its spread. Also, Christians remain a decided minority among the country's population. In addition, under current leader Xi Jinping, the Communist Party has dramatically stepped up its efforts to promote "patriotism" (i.e., devotion to the ideology of the Party). Furthermore, a focus on material well-being continues to be the main concern for many Chinese, not spiritual matters. And yet, it is nonetheless clear that--despite the expectations of many at the time--the establishment of a Communist regime in China was far from being the death-knell for Christianity in that country.
Image: Christian church in Changsha, China, from Wikimedia Commons