Beijing, China - Three decades ago, China's Cultural Revolution saw some of the most dramatic restrictions on the practice of religion ever seen in the modern world.
But today's communist rulers have radically altered their views about religion and have granted substantial freedom to Christians prepared to worship within state-sanctioned churches.
Within these boundaries, Christianity is growing in China as never before - and doing so supported by millions of dollars of government funding.
The BBC has been given unprecedented access to China's state-sanctioned Protestant and Catholic churches, to examine why the government seems so keen to invest in religion.
State funding
On the outskirts of Nanjing, a building site illustrates the scale of the communist state's commitment to supporting the development of Christianity.
Local officials say that the building under construction will become China's largest state-sanctioned church - with space for 5,000 worshippers.
The land - and 20% of the building costs - are being provided not by local Christians, but by the municipal government.
It represents state financial support worth millions of dollars - just one example of the strategy to encourage the development of religion in China.
The Communist Party's senior official with responsibility for this policy is the director general of the State Administration for Religious Affairs, Wang Zuo An.
In a rare interview, he told me that there are now at least 20m Protestant Christians in China worshipping in the state-sanctioned church.
"Such growth is unprecedented in the history of Christianity in China. Christianity is enjoying its best period of growth in China," he said.
And he explained why the Chinese state is investing in religious faith - support which has included funding the construction of national Protestant and Catholic seminaries educating hundreds of future Christian leaders each year.
"Our goal in supporting these religions in developing religious education is that we hope they can train qualified clergy members so that their religions can enjoy better development."
But there is no small irony in the party's new-found enthusiasm for supporting the development of religion in China, given Communism's commitment to atheism.
"On the question of whether there is God, the Chinese Communist Party believes there is no God in the world," said Mr Wang.
"The Communist Party believes that it should respect and protect religious belief. The members of the party must respect religious followers and not infringe their interests."
He insists that there is no contradiction between the Communist Party insisting that its own members are non-religious, and the communist government's commitment to investing in religious development.
"We are making laws and regulations to better guarantee religious belief in China," he says.
Social role
At the Chinese Academy of Social Sciences, a professor who specialises in the study of Christianity believes that there are various factors contributing to its growth.
Professor Xhuo Xinping says that there is a spiritual appeal, and a potential association with economic prosperity.
But he says Christianity will finally shake off imperialist associations if churches are prepared to act as a servant to Chinese society.
"Many Christians pay special attention to social work and social service. I think this is the correct way for Christianity to develop," he said.
One Catholic priest who has pioneered such work in China is the Rev John Zhang - whose Jinde charities receive support from Catholics around the world.
I visited the old people's home he runs in Shijiazhuang City, where he told me why he thinks the government welcomes the church's contribution.
"Homes for the aged are urgent. We need more and more. The government realised that."
"Some officials say, you have done for Chinese society what we cannot do. Without any political involvement, the church is doing a good job, and we from government appreciate it," said Father Zhang.
The enthusiasm of the communist authorities for his church-run initiative is such that even the Communist Youth League used the old people's home as a base for a charitable project.
Confident Christians
But there is still a question about whether as China's Christians grow in confidence they will be prepared to continue to accept the limitations on their freedom.
At Beijing's Haidian Church, the Senior Pastor Wu Weiqing is candid about the problems he faces, but also enthusiastic about the level of religious liberty he enjoys.
"We do have problems, struggling with some kind of regulations, I have to be true to you. But because we are registered, because we obey the regulations and laws, we enjoy more freedom.
"I'm very happy, I enjoy my service as a pastor. I sometimes encourage people who work for the so-called house churches to come to this kind of church to worship," said Pastor Wu.
Those house churches - the unregistered, or underground churches, which were the only place to worship during the repression of the Cultural Revolution - remain a significant part of the Chinese Christian landscape.
But both the Catholic and Protestant churches sanctioned by the state are now also seeing levels of growth that few predicted in the 1980s.
Two students I met at an evening service of prayer and praise at Haidian church summed up the optimism felt by growing numbers of young Chinese Christians.
"We truly hope [that in] our country there will be more Christians, and God's word will spread everywhere in our country", said Daniel.
His fellow student Jesse added, "I think this nation will change, and I think God is doing great things in China."
There is no doubting the confidence of these Christians.
But there is also no guarantee about the sort of future the communist government will allow the churches it is currently keen to support.
To hear more about state-sanctioned Christianity in China, tune in to this week's Heart and Soul on the BBC World Service at 1230 GMT on Wednesday 25 August.