According to a new survey of 50,000 Iranians—90 percent residing in Iran— 1.5 percent identified as Christian.

Extrapolating over Iran’s population of approximately 50 million literate adults yields at least 750,000 believers. According to the researchers, the number of Christians in Iran is “without doubt in the order of magnitude of several hundreds of thousands and growing beyond a million.”

Christian experts surveyed by Christianity Today expressed little surprise. But it may make a significant difference for the Iranian church.

Some said the growth would lead to a massive secularization of Iranian society as a whole. Others pointed out that a free Iran would see an implosion of Islam, and a very significant rise of Christianity and atheism.

There was also concern among some of these experts that the growth is “outpacing discipleship,” and the problem is made worse by the fact that many Christian leaders are now in prison, or have been forced out of the country.

But similar to what has been seen in China, and other countries that persecute Christians, when ministry is forced underground it “spreads like wildfire” through cell groups and house churches.

The result, Iranian authorities have lost oversight of the church and there is nothing they can do to stop the spread of the gospel.