Why is there such a stubborn presence of faith-based activists among the intervenors, pleading for the chance to say no to gay marriage? First, the sacred nature of marriage brings faith communities to the court. "Humans aren't suited to marriage," Phil Epstein, one of Canada's top divorce lawyers, remarked recently. He reminded me that it takes a miracle to keep a marriage together (and I don't have to look far for proof). Millions of Canadians don't think marriage should be messed with because it was not designed by humans. It was a God thing (no invention of it is recorded in law or politics), a spiritual reality. And now, it is being reconsidered by a secular court and government in post-Christian Canada.

Some complain the designs of God are no longer relevant. In fact, intervenor faith groups base some of their case on social care and religious freedoms rather than theology. But behind it all, God's view of marriage is a key reason why both sides are before the court. Gay couples are fighting for the banishing of religious boundaries that keep them from marriage.

When biblical-era critics tried to test Jesus's sense of justice, they poked at his view of marriage, opening one of the best windows into the sacred nature of marriage that we have. The story is found in Matthew 19. In The Message, a contemporary-language version of the Bible, scholar Eugene Peterson records the exchange: " 'Haven't you read in your Bible that the Creator originally made man and woman for each other, male and female?' asks Jesus. 'And because of this, a man leaves father and mother and is firmly bonded to his wife, becoming one flesh -- no longer two bodies but one. Because God created this organic union of the two sexes, no one should desecrate His art by cutting them apart.' "

Moses faced cultural realities that meant the art would have to be cut apart, so divorce became the first legal change to marriage. In Matthew 19, Jesus explains the divorce change was a "concession to your hardheartedness, but it is not part of God's original plan."

If we are at another epic moment of concession, many Christians aren't going to let it pass without a national call to prayer and intervention. One group of Christian academics and activists, the Working Group on Civil Unions, will argue before the court that if marriage is not maintained as a heterosexual institution, then churches should no longer act as servants of the state on marriage. Let the state offer civil unions; allow religious groups to maintain the integrity of their beliefs by offering the marriage ceremony only for those who embrace their marriage doctrine and want to be committed "before the eyes of God."

If the state handled civil unions, it would solve the equality concerns of same-sex couples -- but if churches move from open-door to protectionist policies, countless other couples would lose a spiritual opportunity.

There's a second reason faith communities are going before the Supreme Court: For centuries, they've been concerned about the family's well-being and protection. The churches, temples and mosques represented by, for example, the Interfaith Coalition, hold a history of knowing what builds mom, dad and kids, even if the kids are gay or more open to homosexuality than their parents. Our groups teach about sex, AIDS, marriage, forgiveness and love, divorce, remarriage, parenting and aging; humankind has relied on such faith communities to mark its rites of passage. These groups may differ on whether gay sex is sin, but all know that family life is fragile -- and its breakdown is the source of humankind's deepest pain.

Newspaper reports say that the number of children entering foster care has risen 65 per cent in the past six years. A recent study from the universities of Toronto and California at Berkeley reports that 10 per cent of North American grandparents have long-term care of their grandchildren. The warning light on how we care for our young is flashing. Faith groups believe redefining marriage will weaken it institutionally as the safest place for children.

"Marriage matters. We cannot simply restructure society for someone's vision of utopia and expect that it will not have long-term, and perhaps irreversible, negative impacts on others; children, religious institutions, and couples themselves," argues Janet Epp Buckingham, director of law and public policy for the three million evangelicals who are part of the Interfaith Coalition.

Out of all this, gay activism has given a gift to Christianity. It has pushed us to start talking, praying and repositioning the way we discuss homosexuality. Our stand on the morality of gay sex hasn't changed, but we Christians are learning how to speak with respect and love. There's a new emphasis on research, coalition-building, and on helping weak marriages and celebrating healthy ones.

What's before the court this week is much more than four questions about the constitutionality of the Liberals' proposed act. The sacred realities present in marriage, and our country's legacy of faith and the family, make the court's decision a turning point for Canada. It's a decision like those faced by Moses and Jesus: Do we step away from God's ideal?