The suggestion sounds ludicrous: How could Christianity be responsible for the all-but-assured triumph of the movement for gay marriage? Aren't the most committed Christians the most passionate defenders of traditional marriage and hence the most ardent opponents of permitting gay couples to marry?

From the overwhelming support for traditional marriage among white evangelical Protestants in the United States to the Catholic Church's definition of homosexuality as "intrinsically disordered" to the black (Catholic and Anglican) Christians of Uganda who have recently worked to pass one of the most draconian anti-gay laws in the world, the answer would seem to be yes.

But things aren't quite so simple. Just flip through the opening pages of everyone's favorite work of secular prophesy — Alexis de Tocqueville's Democracy in America (1835–1840) — and you'll find a provocative alternative interpretation of Christianity's indispensable role in the creation of the revolutionary ideal of human equality. The stunningly rapid rise of support for gay marriage over the past two decades is just the latest in a very long line of victories for that consummately Christian ideal — and it's unlikely to be the last.

Tocqueville begins the introduction to his two-volume study of American democracy by noting that "a great democratic revolution is taking place among us." The 700-page book is his attempt to make sense of this revolution, which was transforming life across the European continent during his lifetime, but which was already far more advanced in the United States by the time of his famous visit in 1831.

For Tocqueville, the march of equality was upending age-old institutions and moral habits "in all the Christian world." It was a "providential fact," by which he meant that there was nothing anybody could do to stop it.

The ultimate source of the democratic revolution — the motor behind its inexorable unfolding — is the figure of Jesus Christ, who taught the equal dignity of all persons, and declared in the Sermon on the Mount that the last shall be first and the first shall be last, and that the meek shall inherit the earth.

These are among the most subversive teachings ever uttered — and according to Tocqueville, Western civilization has been working out their logic for the better part of two millennia, as political communities have applied Christ's egalitarian teachings in stricter and stricter terms.

First, the rigidly hierarchical order of the Roman Empire assimilated and transformed Christ's message, creating a series of stratified Christian aristocracies that ruled Europe for centuries. But by the 11th century, the clergy, which "opened its ranks to all, to the poor and to the rich, to the commoner and to the lord," had gained political power. In this way, the principle of equality began to "penetrate through the church to the heart of government."

Over the next 700 years, as Tocqueville tells it, "a double revolution" transpired: "The noble has fallen on the social ladder, and the commoner has risen; the one descends, the other climbs. Each half century brings them nearer, and soon they are going to touch."

They already did touch in the United States, the world's first nation settled by egalitarian Christians (the Puritans) and explicitly dedicated in its founding documents to the principle of universal human equality. Where France required a violent revolution to overturn recalcitrant elements within its social order and advance the cause of equality, the United States merely needed to declare and secure its independence from a foreign power, before allowing the egalitarianism already implicit in its habits and institutions to flower and flourish.

Tocqueville was fascinated by the question of what democracy in America would look like, because he thought it was inevitable that the rest of Western civilization would soon follow it in building societies dedicated to equality. But he was also filled with "a sort of religious terror...by the sight of this irresistible revolution that for so many centuries has marched over all obstacles, and that one sees still advancing today amid the ruins it has made."

Roughly 80 years before the fictional lords and ladies of Downton Abbey begin to realize it, Tocqueville understood that the world of aristocratic privileges was slipping away and would soon be reduced to ruins. That is what inspired his religious terror.

The same terror grips opponents of gay marriage today, as the Christian principle of equality overturns and transforms the Christian tradition's historic understanding of what a marital partnership is and can be. In this sense, at least, opposition to gay marriage parallels an earlier generation's opposition to interracial marriage. In both cases, the opponents of change are attempting to stand against the march of equality. In both cases, the opponents will fail.

By all means, let's ensure that the religious rights of these opponents are protected. But let's also hope that they will eventually follow Tocqueville's example in recognizing that a major reason why equality always wins is that the new order is always more just than what preceded it. This is why Tocqueville counseled resignation and acceptance rather than a reactionary response — because, he concluded, trying to "stop democracy...[is] to struggle against God himself."

None of this means anything as crude as "Christ wants gay marriage." But it does mean that we live in a culture in which reformers who successfully claim the mantle of equality inevitably triumph — because those who oppose equality find it impossible to gain public traction for their own side of the argument.

Equality always wins. And equality became the lodestar of Western culture thanks to Christianity.