The percentage of people who grew up in non-religious families is growing. These folks tend to remain non-religious and fewer of them are marrying people who are religious. This means that we entering the second, perhaps the third generation, of people who have no first-hand familiarity with the basic function or teachings of religion.
Daniel Cox, Research Director, Public Religion Research Institute, writes in the Huffington Post:
[T]here are signs that nonreligious identity is proving more durable, the result of increasing religious diversity, shifting marriage patterns and growing acceptance of nonreligious people. By the 1990s, the majority of Americans who were raised unaffiliated remained that way as adults. In the decade that followed, commitment among the religiously unaffiliated approached that of members of established religions. In 2012, more than 6-in-10 (61 percent) Americans raised unaffiliated were still without religion in adulthood. In comparison, two-thirds (66 percent) of Catholic adolescents remained Catholic as adults during this same time period.
Previous research has shown that marriage often serves to re-engage the religiously unaffiliated, particularly for men who tend to disaffiliate in higher numbers. But here, too, there is evidence that an institution, which previously reinforced religious identity, may now serve to reinforce secular beliefs. In the 1970s only 37 percent of unaffiliated Americans who were married had unaffiliated spouses. By 2010, a majority (54 percent) of unaffiliated Americans who were married reported that their spouse was also unaffiliated. That’s still lower than the rate of religious homogamy among Catholics (76 percent), and Protestants (84 percent), but a dramatic increase all the same. Nonreligious Americans also are using religious identity as an important metric in selecting a partner. When picking a potential mate, nonreligious online daters are demonstrating a strong preference for those with similar religious beliefs.
The increasing number of Americans raised in nonreligious homes presents a significant challenge to churches. Instead of luring back those who were once part of a religious community, they now face the prospect of trying to attract those with no formative religious experiences to draw on. Moreover, Americans with no formative religious experience often have very different expectations and attitudes about religion that are drawn not from personal experience in church, but from the views of friends, family, and also popular culture.