When Islamic terrorists slammed two hijacked planes onto the World Trade Center's Twin Towers, toppling them 15 years ago, they could not have foreseen that their action would help Christian missionaries bring the Gospel to more people in the Muslim world.

Following the Sept. 11, 2001 terrorist attack on the United States, Christian missionaries were able to reach out to more Muslims, according to Baptist Press.

Nik Ripken, a Christian missionary in the Muslim world, said after 9/11 the "trickle of Muslims coming to Christ" became "tens of thousands."

Mike Edens, a professor of Islamic studies at New Orleans Baptist Theological Seminary, said the Sept. 11 terrorist attack inspired a more widespread interest in the concept of establishing links with the so-called "unreached people groups" in an area spanning parts of Europe, Africa and Asia populated by 865 million Muslims. These are areas where people have little or no access to the Gospel.

As Western evangelicals became more eager to share the Gospel with Muslims, parts of the Islamic community became more open to receive it, said Pastor Mokhles Hanna of the Atlanta-area Arabic Baptist Church in Lilburn.

"When Sept. 11 happened, when ISIS came, when al-Qaeda came," some Muslims "started reading more about whether [terrorism and violence] was really the teaching of Islam," Hanna told Baptist Press. "Some of them started realising, 'Wow, this is the Islam we didn't know. ... Muhammad killed. His followers killed. And this is what the Quran is teaching.'"

Because of this realisation, thousands of these enlightened Muslims left Islam, Hanna said, with some becoming secular or atheist and others turning to Christ.

Hanna said despite the flood of Muslims coming to Christ, he is surprised why Christians in the U.S. haven't responded to Muslim spiritual openness with greater Gospel witness.

"It surprises me that American churches still don't get it," he said. "They still don't understand the true nature of Islam and how much more work we need to do to reach out to them."

Former Southern Baptist missionary David Garrison said 9/11 is just one of many factors that have compelled some Muslims to abandon their faith. Other factors include the terrorist campaigns of Islamic State, Hamas, al-Qaeda and Boko Haram.

He said 9/11 awoke Muslims "with a jolt," prompting them to ask themselves, "Is this who we are? If this is who we are, then I'm not sure I signed up for this."