One thing the Islamic Republic appears not to have considered at its birth was that many people do not like being told what to believe and find the official link between faith and politics to be offensive. This has prompt a significant minority of Iranians to look elsewhere for religious satisfaction.
By all accounts the largest growth is with Sufi mysticism. A Muslim does not leave Islam by turning to Sufism, but he leaves the state-approved version of Islam. By many accounts, there are now a few million Sufi adherents in Iran, though firm statistics are impossible to obtain.
The government has had a crackdown on Sufism underway the last several years as it tries to discourage citizens from turning to Sufism.
There is no indication of any measurable growth in the number of Sunni adherents among Persians. Sunnism may be too linked to Arabs and to other minority groups in Iran to be attractive to ethnic Persians.
With regard to Zoroastrianism, the attraction appears to be more nationalist than religious. 
Zoroastrians are not claiming a growth in membership. What is visible is the increasing use of Zoroastrian symbols in jewelry, posters and other displays. Many Iranians appear to be resorting to such symbolism as a form of modest and non-violent rebellion against state dictates. The Zoroastrian symbols represent, to many Iranians, not a faith so much as the long history of Iran before the Islamic era.
Christianity is also growing in appeal. But unlike the turn to Sufism or Zoroastrian symbolism, the shift to Christianity is a volcanic shift that involves total rejection of the state faith and great personal risk. It also implies a turn toward the West.
The Iranian government’s tracking of Christians in Iran has intensified over the last several months, according to Open Doors USA, an organization that provides help to persecuted Christians worldwide.
The numbers are obscure. The new US annual report on religious persecution around the world estimated there were only 10,000 Protestants in Iran. But Open Doors estimates that there are 350,000 Christians from a Muslim background in Iran. This shows the difficulty of dealing with such numbers on religious persuasion.
Michael Wood, an American who works in the Middle East office of Open Doors USA, told The Christian Post that Iran’s house church movement—so-called because adherents usually meet and worship in someone’s home, not in a formal church structure—is one of the fastest growing in the world.
He also said the Iranian government is doing its best to squelch the movement. “Over the last few months, they have made a really strong attempt to undermine what’s going on in the house church movement. They are tearing apart meeting places. If they find out somebody has been involved in a house church group they are arrested or really intimidated,” Wood said. “They are listened to on their cell phones. Houses will be broken into and Bibles and Christian material will be confiscated.
“So, you have a lot of intimidation factors where they are really trying to stifle and minimize the growth of the house church in the country,” he added.
One of the Christian leaders, whom Open Doors did not name for security reasons, said that “things are increasingly getting more difficult”.
“I am allowed to take care of my church members, but I am not allowed to receive other Iranians or to disciple them, while many are coming to Christ. Christian leaders are very careful and also feel uncertain with the growth of Christians and converts in the country. We can hardly handle the growing number of new believers.”
Wood said house church leaders need to be careful about admitting new members into their group because government spies are portraying themselves as people seeking to learn about Christianity in order to entrap Christians for proselytizing.
Wood distributes Bibles and Christian material to house church leaders. However, he said the most effective method of teaching has been through broadcasts from stations based outside Iran. That is also a big difference between the Christian appeal and the Sufi and Zoroastrian appeal.
“We heavily use radio broadcasts, short wave and satellite TV broadcasts to send programs back into the country that are used in house church groups,” Wood said.
Although many house church leaders say they hope for a more open society in Iran, in the same breath they say they would be apprehensive about being allowed to live in a Western society, where Christianity can simply be a label and not a matter of faith chastened by the threat of persecution, Wood said.
“The growth of the church in the country right now is spurred on by the fact that the country is closed and [by] the government’s hostility towards Christianity,” Wood said. “If you look at church history, the great movements of God have come when the church has come under a great deal of persecution. You see a tremendous growth under pressure.”
That also recalls the concerns of the late Archbishop Manukian, the one-time leader of Armenians in Tehran. After the revolution, he pleaded with members of his flock not to move to California. He said the oppression they were suffering in Iran was good for their faith and helped to solidify Armenian Christianity. If they moved to California, he said, they would be treated wonderfully but would soon become Americans more than Armenians.
Many in the Iranian Jewish community have also commented that the Islamic Republic’s coercion has made those Jews who remain in Iran far more religious than they ever were before the revolution.
