JUDAISM AND Islam developed with only marginal reference to Christianity, but Christianity’s evolution has been entangled with the two other monotheisms — as essential foils. That has nowhere been more evident than in the Middle East. European Christendom came into existence in tension with an imagined “Holy Land’’ to which both Jews and Muslims had competing claims. That competition continues — sometimes dangerously, as on the Israeli-Lebanese border last week. If the current Obama push toward a revitalized peace process succeeds, with Palestinian and Israeli negotiators re-convening, ghosts in the room will have Christian origins. The way to render those ghosts harmless is to identify them.

Rabbinic Judaism and Christianity began as rivals, but they were comparably despised minorities in the pagan Roman Empire. Then, with the conversion of the emperor Constantine (310), the empire became Christian, and the church began to reinforce its claims with the power of the state. Heresy became a capital crime, and those who rejected, say, the doctrine of Christ’s divinity were put to death. Jews came under harsher scrutiny, too. How ludicrous, the thought went, that Christians were killed for dissenting from theological technicalities, while Jews, who disdained the whole of Christian belief, were allowed to live. By the end of the 4th century, prelates like Ambrose of Milan advocated violence against Jews, effectively offering them the choice of conversion or death. This was immediately opposed by the only figure with stature sufficient to challenge Ambrose — St. Augustine, who cited a psalm in defense of Jews, “Do not slay them!’’

Instead, Augustine argued that Jews should be allowed to survive within Christendom as Jews. (But for Augustine’s “lovely brainwave,’’ as the 18th-century Jewish philosopher Moses Mendelssohn put it, “we would have been exterminated long ago.’’) But this was a defense with a catch. Jews were to survive, but never to thrive. Permanently in exile from their homeland, they would, in Augustine’s formula, be a wandering “witness people’’ whose homeless misery would demonstrate the truth of the very Christian claims they rejected. When Christians were in control of Jerusalem, they almost never allowed Jews to reside there — not merely out of bigotry, but because, after Augustine, Jewish exile was a matter of theological proof.