Bishop Salvatore Cordileone has been strongly involved in Californians’ efforts to preserve the definition of marriage as the union between one man and one woman.

Now, the bishop of Oakland, Calif., has become chairman of the U.S. Bishops’ Ad Hoc Committee for the Defense of Marriage, and he will be working to promote traditional marriage in the face of legislative efforts to legalize same-sex “marriage.”

You have called marriage and the family “the most vital and defining issue of our day.” Why?

For a society to be thriving and strong, it has to rely on citizens who are honest, virtuous, industrious and able to fulfill their promises. And where do people get their education, in the full sense of education, not just in the sense of imparting knowledge? Primarily in their families. So solid marriages and families are essential to a thriving society.

What’s the cornerstone of marriage between a woman and a man?

The reality of marriage as the union of a mother and a father is grounded in our very biology. A child comes into the world by the union of a man and a woman. That’s a basic biological fact that cannot be denied. There’s a mother and a father for every child.

What do Catholics most need to understand to enter reasonably and effectively into the public debate over marriage in our society?

Our people need to understand what’s really at stake here, and that’s the very concept of marriage itself. Is it a relationship to be defined by adults for their mutual benefit and enjoyment? Or is it a relationship to bring children into the world and to provide them with the best possible context for their well-being and education?

If it’s first and foremost about children, then we’ll want children to be connected to their mothers and fathers.

The definition of marriage as a relationship that exists “solely for the benefit of adults,” you point out, is an extremely recent development. In an interview on EWTN, you cited it as “the greatest error of our times.”

It’s a completely novel concept. From the beginning of the human race, up until a few years ago, marriage has been understood as the best possible context for raising children, for giving children what they need, so they can be protected and nurtured.

Why exclude people of the same sex as heads of a family?

Because children need, deserve and long for a mother and a father. The optimal situation for children is to be raised by the man and the woman who brought them into the world in a loving, committed, stable relationship.

Many studies show the role of the father figure — just the presence of the father figure in the family — is especially critical. Children need that. When they don’t have it, they long for it.

As someone wiser than I put it, when a child is born, the mother is sure to be nearby. There’s no guarantee the father will be nearby. Society needs a cultural mechanism to connect fathers to their children, and that mechanism is marriage.

Where does this error of thinking about marriage as “solely for the benefit of adults” come from?

Well, if you trace it back far enough, I’m convinced it comes from the contraceptive mentality.

The Church has always understood that the two ends of marriage are: first, the procreation and education of offspring and, second, the union of the man and the woman for the mutual good of the two spouses. They’re inseparable. The contraceptive mentality, however, attempts to separate those two.

When contraception became much more available and prevalent because of marketing, as well as technology in the ’60s, we began to see much more sexual promiscuity. With more promiscuity, you have more children born out of wedlock. Because contraception is not perfect — it misfires, so to speak — children are conceived, so now we need abortion as a backup. We also see a rise in divorce.

What’s essential to the definition of marriage?

The Church has long understood the three “goods” of marriage as defining what is essential to marriage. Those three “goods” — the language comes from St. Augustine — are procreation, fidelity and permanence.

So how has the contraceptive mentality eaten away at this essential definition?

With the contraceptive mentality, we saw sexual promiscuity, which led to the novel concept of so-called “open” marriages. That strikes down the good of fidelity in marriage. Then we saw couples entering into marriage without any intention of having children, so that strikes down procreation. And in the early ’70s, we had states passing laws allowing for no-fault divorce. When we’re in a divorce culture rather than a marriage culture, that strikes down the permanence of marriage.

So, this erosion of the meaning of marriage has been going on for a very long time.

And now we’re facing same-sex “marriage.”

It’s the latest and, I would say, most drastic, episode in this long-term erosion of the meaning of marriage.

What’s the result of emotionally changing the definition of marriage away from the way it has been reasonably understood since the beginning of the human race?

The result of changing its definition is that marriage becomes drained of all meaning, because it can be defined in any way the people involved want to define it. If we start changing what is essential to marriage in its definition, then there is no end to it. If it doesn’t have to be a man and a woman, why does it have to be two people? Can’t there be several partners, male and female, in a marriage? Who’s to say it should be limited to two? So what is the point of government giving benefits to married people?

When we defend marriage between a man and a woman, our opponents say we’re just imposing our religion on everyone else. What’s the answer to that?

This is not a matter of religion. This is how every society has understood marriage in all of human history. The truth is: They’re imposing their new idea of marriage — an idea no society has ever had before — on everyone else. This is a very serious social experiment that will have dire consequences.

The Church plainly has the clarity of thinking we need to build a new marriage culture. How are we going to work together to get the word out?

The pulpit is one key means, and I would hope to see homily resources for catechesis on marriage. The U.S. bishops’ conference is currently working on a video series that can be used for catechesis called “Marriage: Unique for a Reason.”

We also need to look into getting this into the curriculum, especially in our high schools and religious-education programs. Stand With Children, a marriage-advocacy program started in California by Catholics for the Common Good, is a great place for lay Catholics to begin.

You said we need a massive educational effort to defend marriage. Where should that begin?

We need to start with young people, teaching them the basic facts of life. The whole way man and woman are designed in nature, all the changes that take place in our bodies — especially the woman’s body — are geared to conceiving a new life and then nurturing that life to birth and even after birth.

Beginning with biology will help our young people better respect their own bodies, and it will lay the groundwork we need to teach them all the other reasons behind the Church’s teaching: the psychology, sociology, developing the virtue to be able to sustain a lifelong committed relationship, the benefits people derive from that relationship personally and the benefits to society. Then we can move out to the theology underlying marriage, the mystical marriage between Christ and the Church. It’s all interconnected. We need to begin with the biology and move out from there.

Sue Ellen Browder writes from Ukiah, California.