Some churches are losing people because they have failed to preach the "real Gospel" and are instead only offering "feel-good moments", apologist Ravi Zacharias has said.
Speaking to Fox News, he said that while evangelicals had "grown in numbers", mainstream churches were struggling because they were drifting from the main message of the Bible.
"Some of the mainliners have lost numbers and they should've lost numbers because they lost the message," he said.
"If you've lost the real Gospel, people are going to say, 'Why am I coming here? Is this an ethical society or a feel-good moment on Sunday morning?'
He said that the growing churches were the ones "where the Gospel message of Jesus Christ is being given to the young and to those who are even thinking seriously about what life is all about".
The popular speaker and author went on to say that there had been a shift in the debate around faith over the last few decades from whether God existed or not, to "more existential" questions.
"All the questions you ask can only be answered after you have found the answer to the first question: Why you actually exist," he said.
"And when you find that relationship with God through Jesus Christ, as I believe, then all the other questions are justified and the answers are forthcoming."
Another change, he noted, had been brought about by the arrival of modern technology and social media, with people increasingly "living in front of a screen and missing out in relationships" despite having more avenues than ever to communicate with each other.
"[S]o the questions are getting larger and larger and the soul is getting emptier and emptier," he said.
A recent survey revealed that for young Americans, religion is increasingly irrelevant.
The study of Americans' most cherished values by the Wall Street Journal and NBC News found that among those aged 24 and younger, only a third felt that religion was important to them, compared to over half of the Baby Boomer generation.
Far more important to young Americans were community and tolerance.