Only 51 percent of American adults are married — a record low — down from 72 percent in 1960, according to a Pew Research Center analysis of Census data.

There are three major factors behind these trends.

First, the number of never-married Americans has almost doubled, from 15 percent to 28 percent, from 1960 to 2010. Pew said that many couples are cohabiting instead of marrying because “they fear divorce.” Why? Many are adult children of divorce who do not want to live through such pain again.

Second, the number of divorced and un-remarried people has grown from 5 percent to 14 percent of the population.

Third, in the last 50 years, the median age at which people first marry has jumped six years — to 26 for women and to 29 for men. Today, only a fifth of adults ages 18 to 29 are married, as opposed to three times as many in 1960, 59 percent.

What’s troubling to me is not the later age at which people marry, which is generally wise, but the fact that so many have never married. Only 72 percent of today’s adults have ever married, versus 85 percent in 1960.

This is a big cultural change. What is behind this shift? Another recent Pew survey reported that four in 10 Americans think marriage is “becoming obsolete.”

What’s particularly interesting is that 47 percent of those who think marriage is becoming obsolete say they would like to marry; virtually the same share (45 percent) of unmarried adults who think marriage is not becoming obsolete say they want to wed.

Those numbers suggest a strategy for churches, who perform nine of 10 weddings: Make a case for marriage from the pulpit. True, there aren’t many cohabiting couples in church, but there are millions of churchgoing parents of adult children who do not know what to say to them.

What are the best arguments that pastors might make about the value of marriage?

I recommend that clergy read “The State of Our Unions: Marriage in America 2011,” by the Institute for American Values. Its co-authors are W. Bradford Wilcox of the National Marriage Project at the University of Virginia and Elizabeth Marquardt of IAV’s Center for Marriage and Families.

Their report, “When Baby Makes Three,” provides scientific evidence of what every pastor has long believed: “Couples who both agree that ‘God is at the center of our marriage’ are at least 26 percentage points more likely to report that they are ‘very happy.’ ” While 50 percent of both men and women report being very happy, of those who believe God is at the center of their marriage, 77 percent of women and 76 percent of men are very happy.

These more religious couples are also more likely to report high levels of commitment and a pattern of generous behavior toward one another. “In other words, marital spirituality is linked to beliefs and behaviors that strengthen the marriage bond,” said the report.

Similarly, mothers and fathers who see parenting as one of “life’s greatest joys” are about twice as likely to reporting being very happy in their marriages. It is one of the “Top Five Predictors of Marital Success.”

However, the report cautions that “parenthood is typically associated with lower levels of marital happiness.” Having a baby requires sacrifices such as a loss of sleep, less disposable income and often less quality time with one another, resulting in less sex.

And there is a sad paradox among young Americans. While most would like to have two or three children, “a growing share of young women and men believe that a good marriage is personally unattainable, and more are raising children outside of marriage.”

However, the report, “When Baby Makes Three,” provides new evidence that both husbands and wives (but wives especially) are “more likely than their childless peers to feel their lives have a sense of meaning and purpose.” And a substantial minority of married couples do not experience parenthood as an obstacle to marital happiness.

What is their secret? Two answers are shared housework chores and sexual satisfaction. One surprise is that the happiest wives and husbands today “are those with no children and those with four or more children.”

Another important factor is education. Americans without college degrees are three times as likely to divorce in the first 10 years of marriage compared with those with college education.

Most important, however, is a shared faith that endows marriage “with transcendent significance.” Attending services together is a top predictor of marital stability.

Finally, “parenthood makes life meaningful and marriage makes parenthood bearable.”

Mike McManus is president and co-chair of Marriage Savers, www.marriagesavers.org.