Young people today, even Christians, frequently told the survey that Christianity today is no longer what it was supposed to be. They say it changed and changed for the worse. And one result of this is a large increase in the numbers of people who are not Christians.

Simply put, each new generation has a larger share of people who are not Christians (that is, atheists, agnostics, people associated with another faith, or those who have essentially no faith orientation). The new book refers to this group as "outsiders" because they are describing what Christianity looks like from an outsider’s perspective. Among adults over the age of 40, only about one-quarter qualify as outsiders, while among the 16 to 29 segment, two-fifths are outsiders. This represents a significant migration away from the dominant role that Christianity has had in America.