The idea of the separation of church and state “began, in fact, with Jesus”, the editor of Newsweek assures us in a May 3 editorial on a federal judge’s recent decision that the National Day of Prayer is unconstitutional. You can probably fill in the rest of the argument, which skims lightly and not altogether coherently from “My kingdom is not of this world” to Paul’s declaration that “in Christ there is neither Jew nor Greek” to free will, before returning to some real authorities: Washington, Jefferson, Adams, and the Treaty of Tripoli.

The editor, Jon Meacham, defends the American religious settlement that created a free religious market “in which religion can take its stand in the culture and in the country without particular help or harm from the government.” Religion doesn’t need government support, since anybody is free to pray whether or not there is a National Day of Prayer.

Violating the American tradition of religious liberty might damage and defile religion, warns Meacham. He hopes that “serious believers, given the choice between a government-sanctioned religious moment and the perpetuation of a culture in which religion can takes its own stand, free from the corruptions of the world,” will do what Jesus did and “choose the garden of the church over the wilderness of the world.”

Which is funny, since I picked up Meacham’s editorial just after finishing a chapter of Paul Veyne’s bracing new When Our World Became Christian (Polity, 2010), which vigorously and learnedly says pretty much the opposite. Throughout his brief study, Veyne, an emeritus professor of Roman history at the College de France and author of such classics as Bread and Circuses and Did the Greeks Believe in Their Myths?, notes the radical difference between paganism and Christianity. Unbeliever though he is, he considers Christianity a “masterpiece” and compares it to a “best-seller” that revealed a “thitherto unsuspected sensibility.” Paganism and Christianity were not different species of the same genus. Christianity belonged to a different genus entirely.

Centrally, Christianity differed from paganism because Christ made absolute claims beyond anything pagan gods dreamt of. Veyne observes that after Augustus defeated Antony and Cleopatra at Actium, he paid his dues to Apollo by building and funding a temple. But Augustus did not believe that Apollo had elected him, nor that he was Apollo’s servant. Like most pagan Romans, Augustus was happy so long as the gods responded to his prayers by giving him political and military victories. In short, “Augustus did not serve Apollo; he simply turned to him for help.”

As evidence of the “contracted and spasmodic” relationships between pagan gods and their followers, Veyne recalls two incidents. When the beloved prince Germanicus died, the plebs attacked temples and knocked down altars. Job’s “the Lord gives and the Lord takes away” was not in their religious vocabulary. If the gods wouldn’t help, the plebs would no longer render them worship. Much later, when Constantine’s descendant Julian (“the Apostate”) lost a battle, he decided he would never sacrifice to Mars again. Pagan devotion was pragmatic, functional, and temporary.

By contrast, the Christian was not concerned about being content with God but “endeavoured to make his God content” with him. Unlike Augustus in relation to Apollo, Constantine spoke of himself as Christ’s servant, and acknowledged that Christ had generously placed him in that position. When Constantine put the Christogram on his soldiers’ shields, most pagans did not understand that “the relationship between this god and his creatures was a permanent, passionate and mutual one.”

This fundamental difference in orientation had political consequences. For pagans, the gods left Caesar pretty much to himself. Emperors wanted the gods on their side, the strong gods especially, but in the fine print of the religious contract, the gods agreed to observe a high-minded policy of non-interference. Pagans had never confused Caesar with the gods, so there was no need to separate them. Pagan religious was ubiquitous, providing pomp and ceremony for important occasions, but the gods did not issue orders to Caesar or anyone else.

Christianity reoriented the relations of God and politics. Christians thought every one should submit to Christ, including Caesar. In place of the superficial veneer of sanctity with which paganism covered Roman politics, Christianity “theorized and systematized” the relation of politics to religion. Because of Christianity, Caesar would no longer be allowed to carry on picking and choosing gods as he pleased. Veyne argues that “God began to weigh heavily upon Caesar and Caesar was now obliged to render to God whatever was his due. Christianity would now expect from princes something that paganism had never demanded: namely, that they ‘make their power a servant to the divine majesty, to spread the worship of God far and wide’” (the quotation is from Augustine).

Veyne concludes, “Contrary to what is frequently claimed, Christianity was further from drawing a distinction between God and Caesar than any other religion” in the fourth century, and beyond.

This is the possibility that Meacham cannot allow himself to contemplate. He can imagine government sponsorship of religion and the religious coercion that frequently has followed, and he recoils. He can imagine religion standing prissily to the side, going to the garden alone, and his heart is strangely warmed. What he cannot imagine is the possibility that Christ might lay demands on Caesar. Yet it’s that third, unthinkable prospect that is inherent to the Christian gospel; it’s that third, unthinkable prospect that marked the political difference between Christianity and paganism.

Meacham believes that the American “creed” of religious liberty implies that Christ and should leave Caesar well alone, and that Caesar should politely return the favor. But Christians have their own creed, and it does not permit mutual indifference of religion and politics. Frightening as it seems to be for Meacham, he must know that “Jesus is Lord” is also in the New Testament. Leaving Caesar alone is just what Jesus does not do.

Peter J. Leithart is a pastor of Trinity Reformed Church in, Moscow, Idaho, and Senior Fellow of Theology and Literature at New St. Andrews College. His next book, Defending Constantine will be published by InterVarsity Press.