Barna has an article entitled, “Casual Christians and the Future of America”. Read it here.
Interestingly enough, in the same “feature articles”, there are two other articles which may give reason to this casual christianity. You can read them here and here.
Dr. Mohler answers some of these articles in a book he has written called Culture Shift. Tim Challies provides an overview of the book here. The book can be purchased here from WTS Bookstore.