Statistics indicate that a growing number of Americans are marrying someone from outside their own religious commitments. Is this a trend we should encourage? Not if you are committed to the Gospel of Jesus Christ.

The statistical trend is clear enough, but the question is more complex than may first appear. The Washington Post reported on June 6, 2010 that 25 percent of American households were mixed-faith in 2006, according to the General Social Survey. That represents a significant increase from the 15 percent of such households in 1988.

But, what does mixed-faith mean? It could mean the mixing of relatively similar Christian denominations, or it might mean the mixing of two very different systems of belief.

As Naomi Schaefer Riley reported, “In a paper published in 1993, Evelyn Lehrer, a professor of economics at the University of Illinois at Chicago, found that if members of two mainline Christian denominations marry, they have a one in five chance of being divorced in five years. A Catholic and a member of an evangelical denomination have a one in three chance. And a Jew and a Christian who marry have a greater than 40 percent chance of being divorced in five years.”

That paper by Professor Lehrer is truly interesting. In “Religious Intermarriage in the United States: Determinants and Trends,” published in the journal Social Science Research, Lehrer acknowledged that the span of differences “corresponds to a continuous variable.” In other words, there is a huge difference between a marriage where a Presbyterian marries an Anglican and one in which a Baptist marries a Mormon.

Lehrer defined a couple as religiously intermarried if, for example, an Evangelical marries a Roman Catholic, or a spouse allied with a liberal Protestant denomination marries someone from “an exclusivist group.” She then allowed, “Unions involving members of two ecumenical Protestant denominations are treated as homogamous.”

All this points to a very interesting pattern. Part of the rise in the statistics about mixed-faith marriages is due to the increasing secularization of the liberal Protestant churches and denominations. To that must be added the huge increase in interfaith marriages among liberal Jews, and the more ecumenically minded among other religious bodies.

Lehrer documented the fact that the more conservative faiths were not intermarrying at rates anywhere near the more liberal groups — and for understandable reasons. When the level of doctrinal commitment is low, the barriers to interfaith marriage are correspondingly far less significant.

Nevertheless, even with all this taken into account, it turns out that marrying outside the faith is one of the most significant risk factors for divorce. Citing the American Religious Identification Survey of 2001, Riley reported that “people who had been in mixed-religion marriages were three times more likely to be divorced or separated than those who were in same-religion marriages.” Riley referred to this fact as “an open secret among academics.”

Professor Lehrer described what she called the “large destabilizing effects” associated with mixed-faith marriages. Why is an interfaith marriage at such risk? The answer, in terms of the academic perspective of Professor Lehrer, is that “religion influences many activities that husband and wife perform jointly.”

Or, as Naomi Schaefer Riley observed, “The differences between husband and wife start to add up.” Seen in the context of the decisions that couples have to make in the course of life together, this is surely an understatement.

Putting all this together, it is clear that theological differences really do matter. These belief systems develop into worldviews that do have real consequences. It is not primarily a matter of which holidays the family observes, but how the children are raised, how the major decisions of life are framed, how the priorities of the couple are aligned.

The sociological evidence points in one clear direction — toward the inherent instability of true mixed-faith marriages. Even among the more liberally minded, the tensions remain.

For Christians, the issue is not settled by sociological data, however. In 2 Corinthians 6:14, the Apostle Paul commands that Christians must “not be unequally yoked with unbelievers.” This command reaches far beyond marriage, but it certainly includes the covenant of marriage within its span. Paul’s principle is clear: The Christian’s commitment to Christ is determinative of his or her other commitments. A believer must not marry an unbeliever, for this violates the very logic of the Gospel and the believer’s union with Christ.

The believer in Christ acknowledges him as Savior and Lord, with an allegiance that exceeds any earthly commitment. When two believers are married, they share this mutual commitment and are commonly dedicated to the Lordship of Christ. Their worldviews and allegiances merge into the strength of mutual discipleship, and the big questions of life are answered by their common faith in Christ.

In contrast, the mixed-faith marriage lacks this mutuality of faith and commitment. Worldview divergences and issues of contrasting beliefs are almost surely to hit where they matter most — in relation to the most significant questions of life.

The sociological research presents a clear case for social concern, but the Christian case against mixed-faith marriage emerged long before the academic discipline of sociology. That case is rooted in the logic of the Gospel itself, and in the reality of the Lordship of Jesus Christ. The Christian case against mixed-faith marriage does not end with the question of marital survival or divorce. To the contrary, the Christian concern about marriage has nothing less than eternity in view.