The Catholic Church has one of the highest “retention rates” of any Christian church in the United States.

A new study by the Pew Forum on Religion and Public Life reported that 68% of Catholics carry their faith into adulthood.

This number is not a cause for celebration; the fact that 32% of Catholics do not live out their faith as adults should be a matter of profound concern. But as Sister Mary Ann Walsh, director of the Office of Media Relations for the U.S. Conference of Catholic Bishops, noted in a column published yesterday by Religion News Service, there is plenty of cause for optimism, too.

Here’s what Sister Mary Ann said in her RNS column:

WASHINGTON — The new “Faith in Flux” study from the Pew Forum on Religion & Public Life will draw groans from many Catholics when they read that “Catholicism has suffered the greatest net loss in the process of religious change.”

No surprise there. With one in 10 Americans a former Catholic, some say that ex-Catholics comprise the second-largest religious group in America.

The Pew study notes that those who have left the Catholic Church as adults outnumber 4-1 those who join in adulthood. However, the same report says that 68% of people who were Catholics as children remain Catholic in adulthood. That’s an impressive retention rate in modern American life.

Think of other affiliations in modern society. Divorcerate.org reports that only 50% of Americans remain married to their first spouse. A “Psychology Today” article reported that about one-third of adults described their relationship with their siblings as “rivalrous or distant.”

This is not to be blasé about the 32% of Catholic children who drift away to another or no faith in adulthood. Certainly it’s a higher loss than that of the Good Shepherd who went off to find the one of the 100 sheep who strayed. And it’s four times more than Jesus’ loss rate among the apostles — one out of 12.

Polled for why they left, 47% of former Catholics cited discontent with such issues as the Church’s position on birth control, homosexuality, and attitude toward women. I don’t take much stock in that since, like it or not, there are plenty of self-identified Catholics who grouse a lot, or even carry picket signs over the Church’s positions, but it doesn’t necessarily drive them away.

The No. 1 reason people leave their childhood religion is that they just slowly fall off. That was true for seven in 10 ex-Protestants and ex-Catholics. Mediocrity is the real killer, as it is in everything.

Interestingly, the study found that the best predictor of people remaining in the Catholic Church in adulthood is childhood and teen Mass attendance.

An old nun once told me she prayed daily that she would be faithful to her vocation — this from a woman who had been a nun for more than 50 years. She was a terrific nun, good to the poor, intellectually curious, an intense pray-er and fun to be with. I drove her to work each morning and we had great conversations, but I was blown away to hear her say that she still prayed to be faithful. I decided then that it might not be such a bad idea. I thought that if my vocation meant anything, I ought to pray for it. Now, when I go into a church for the first time, and recall the Irish belief that you get three wishes on such occasions, one is always for fidelity to my vocation. (I get to a lot of churches in my line of work.)

I offer this aside because it suggests that if you value something, you work at it. If you value your Catholic faith (and hope your children will too), you work at it by placing a premium on Mass attendance.

Someone once said that it is not that Christianity has been tried and failed; it’s never really been tried. A lot of people who are counted as Catholics have never given Catholicism a try. They were baptized and confirmed, but outside of those experiences were hardly ever in church. The study’s finding that the best predictor of children remaining in the Catholic Church is Mass attendance seems to confirm the connection between really “trying” the Catholic faith and staying with it.

The challenge for the Church, of course, is to make Sunday Mass attractive. Ingredients on the celebrant’s part include conveying a sense of reverence, providing for well-read Scriptures that all can hear, and delivering a decent homily to carry people through the week.

That, and a bit of purposefulness on the part of congregants in just getting there, will go a long way in turning some of these numbers around.

Meanwhile, Catholicism’s 68% retention rate in today’s world isn’t bad.