The father of the bride was a member of my church and so I was invited to take part in the wedding. But the ceremony was Jewish so a rabbi did the bulk knot tying.

We were on a hill overlooking the Pacific Ocean with a cool breeze and glorious sunshine, but that’s not what made the wedding memorable. It was the rabbi’s explanation of the chuppah, the cloth canopy under which Jewish couples are married.

Your chuppah, he told the couple, is a tablecloth. Don’t tuck it away for rare special occasions. Use it. Use it every week as you and your family gather for Sabbath dinner. And yes, he added, in case somebody missed his point, we expect you to have children.

I was stunned. Linking marriage and children. Can you imagine? Most ministers apparently can’t. I may have changed my ways (and did), but my wife and I have attended many weddings since then (we’re at the age when our friends' children are marrying) and I haven’t heard a single minister mention the expectation of that the couple will have children. It’s as though we’ve adopted the notion that marriage is about the happy couple’s lifelong companionship and nothing else.

It’s a big mistake for which we are now paying a high price.

This week the Supreme Court heard two cases about redefining marriage to include same-sex couples. During the first, the justices seemed to latch onto the argument that same-sex marriage is a vast social experiment with unknowable consequences some of which may be bad. But they paid little attention to the central argument that defenders of traditional marriage are making: marriage is about the begetting and rearing children.

Reporting for World, Emily Belz wrote that in his defense of marriage, “[attorney Charles] Cooper’s arguments about the government’s interest in protecting traditional marriage because it alone results in procreation did not gain much traction. Same-sex marriage, he said, would ‘refocus the purpose of marriage away from the raising of children to the emotional needs of adults.’ The justices pointed out, in not so many words, that heterosexual marriage is already commonly divorced from the purpose of procreation.”

And indeed it is.

Couples — including Christian couples — feel free to marry with no intentions of ever having children. Contraception and easy sterilization (tubal ligations and vasectomies) made this possible years ago and we think nothing of it. Couples who choose non-procreation, that is, who choose to remain childless, have marriages that are about nothing more than mutual love, commitment and companionship. That’s quite a lot, you say. It is quite a lot. It’s also precisely what same-sex marriage advocates are seeking in their necessarily non-procreative marriages.

We’ve walked into the trap. If procreation is not a part of the nature of marriage and thus required for those who are able to procreate, there is no good reason for denying marriage to same-sex couples.

So in our rush to defend one-man-one-woman marriage, we’ve rediscovered the truth about marriage we’ve been ignoring and that I heard from the rabbi on the California coast. A wedding creates the nucleus of a family that is intended by its nature to grow through procreation. Either that or Genesis 1:28 no longer applies.

It’s not hard to understand, but in our individualistic culture it’s hard to take to heart and hard to communicate to others. So can we do?

First, get the facts. The arguments for traditional marriage are summarized in the free download "What You Need to Know About Marriage" by the Alliance Defending Freedom, Family Research Council, National Organization for Marriage and the Heritage Foundation. Download it and read it.

Second, if marriage is about procreation and the rearing children, then Christians need to marry, procreate and bring up godly children. What are we waiting for? And pastors in pre-marital counseling and at the altar need to be as bold and direct as my rabbi friend, “We expect you to have children.” Married couples should take them seriously.

Third, don’t give up. The debate over the meaning of marriage will be with us for decades, we’re starting from a position of weakness, and the culture is tone-deaf to this line of thinking. Don’t give up, but instead, beginning in our families and churches, participate in the rebuilding of a culture of marriage, a culture as beautiful as a clear sunny day on a hill above the Pacific.