The megachurch formerly pastored by I Kissed Dating Goodbye author Joshua Harris has asked Christians to pray that he finds "redemption and restoration" after he revealed he was separating from his wife and had fallen away from the faith. 

Harris left many Christians reeling after announcing on Instagram that he and his wife of 21 years, Shannon, had decided to continue life together "as friends". 

But there was no hint of the even more explosive revelation to come a week later when he admitted that he was no longer a Christian. 

In the latter post, he also revealed a surprising about-turn on homosexuality and announced that he now supported marriage equality. 

"My heart is full of gratitude. I wish you could see all the messages people sent me after the announcement of my divorce. They are expressions of love though they are saddened or even strongly disapprove of the decision," he said on Instagram.

"I am learning that no group has the market cornered on grace. This week I've received grace from Christians, atheists, evangelicals, exvangelicals, straight people, LGBTQ people, and everyone in-between. Of course there have also been strong words of rebuke from religious people.

"While not always pleasant, I know they are seeking to love me. There have also been spiteful, hateful comments that angered and hurt me.

"The information that was left out of our announcement is that I have undergone a massive shift in regard to my faith in Jesus. The popular phrase for this is 'deconstruction,' the biblical phrase is 'falling away.' By all the measurements that I have for defining a Christian, I am not a Christian.

"Many people tell me that there is a different way to practise faith and I want to remain open to this, but I'm not there now."

In the bombshell updates, Harris also confirmed that he had decided to withdraw I Kissed Dating Goodbye from circulation.

The book was published in 1997 and became a bestseller in Christian circles with its strong call to purity and abstinence not only from sex but even from dating.

Despite the huge influence of the book, he later said he had undergone a "reevaluation" of his ideas.

"I no longer agree with its central idea that dating should be avoided. I now think dating can be a healthy part of a person developing relationally and learning the qualities that matter most in a partner," he said.

Covenant Life, in Maryland, the megachurch pastored by Harris from 2004 to 2015, has responded to the updates in a letter to the congregation that was later posted online by investigative journalist Julie Roys.

"These updates are hard to hear. We love Josh and Shannon. For most of us, Josh isn't just some distant public figure," wrote Rogers.

"He's a beloved former pastor and friend. So this news isn't just a lot to process theoretically. It hits home personally."

He said that after hearing the news of Harris' separation from his wife, he turned to 1 Timothy. 

"Several times Paul mentions former Christian leaders 'swerving from,' 'wandering from,' or 'making shipwreck' of their faith. So while this is sad and confusing, it isn't new," said Rogers.

"Paul says some had gone off course theologically. Others behaved in ways that violated Christian conscience. For others, it was greed. In every case, Paul's hope was for redemption and restoration.

"That these leaders would develop 'love that issues from a pure heart and a good conscience and a sincere faith.' (1 Tim 1:5) That should be our hope and prayer for Josh as well."

He went on to ask that the congregation pray for Harris.