The more things change, the more they stay the same. Only a generation ago, the pope from Poland, John Paul II, was nearly assassinated for mustering his church’s vast religious and rhetorical arsenal to confront European communism, a totalitarian ideology that stood opposed to Catholicism’s understanding of the natures of God and man and the relationship between the two. Today, John Paul’s successor, Benedict XVI, finds himself under beefed-up guard amid fears that an attempt might be made on his life, for the “crime” of articulating a challenge for Islamic theologians.

That challenge, as Daniel Johnson observes nearby, is to find a way for Islam to coexist peaceably in a pluralistic world. This is a pressing question not just in Europe, or along Israel’s borders, or in regions of Africa where Islamists are attacking Christians, but everywhere airplanes bring foreigners into the city and television and satellite dishes bring other cultures into the living room. In an age when radical Islamism is turning to violence instead of reconciliation, the pope’s question is one of war and peace, although Benedict said so only obliquely in his remarks last week at Regensburg University.

Benedict’s teachings are both similar to and different from John Paul II’s struggle with communism. John Paul recognized the mortal threat to the west, to human dignity, and to all religion, including his own, posed by communism. Benedict understands that his flock faces a similar existential threat at the hands of a violent subset of nihilistic Islamic believers. Yet Benedict also recognizes that the new struggle requires a different approach. While John Paul’s fight understood that communism could never coexist with western or Catholic values, Benedict is not rejecting coexistence with Islam. He has responded to the Islamist furor over his initial remarks by calling for “frank dialogue, with mutual respect.”

Mr. Johnson suggests that Benedict is uniquely qualified to represent western Christianity in such a dialogue. The Roman Catholic Church Benedict leads is similarly qualified. Over its 2,000-year history, Catholicism, like Islam, has struggled to maintain its integrity under bombardment from an array of cultural, philosophical, and scientific forces. The bulk of Benedict’s speech at Regensburg was not about Islam at all — it was about Christianity, and about how Christian notions of the evils of using violence to spread religion have developed in the context of a debate about the influence of secular Greek philosophy on Christian faith.

While the current pope, though holding fast to his belief in the truth of his own faith, is willing to converse with his antagonists in a way the nature of communism never allowed John Paul II to do, the result appears to be the same. Merely raising the question has already cost the lives of some Christians at the hands of radical Islamists, possibly including a nun in Somalia, and several churches have been firebombed. John Paul II was nearly killed by a plot orchestrated by the Kremlin, and Vatican authorities evidently fear a similar attack against Benedict and have increased his security detail accordingly.

We may not know for a generation or more whether Islam as a whole will be able to sublimate its fanatical wing, although the fact that many Muslims do live peaceably alongside non-Muslim neighbors gives some grounds for hope. Certainly Benedict’s challenge at Regensburg was, at heart, an optimistic one, offered in the belief that Islamic scholars will rise to it. Oriana Fallaci, who died last week, was not nearly as optimistic, criticizing Benedict for “insisting on that monologue with dismaying hope” even while she praised him for appreciating the stakes of the fight.

The current pope, like his predecessor, is fighting a two-front war. He must take on radicals outside his faith while also convincing his co-religionists of the seriousness of the fight. In this sense, Benedict’s decision to quote the Byzantine emperor Manuel II Paleologus is an apt one. Manuel was the penultimate eastern emperor, who presided over a drastically diminished realm in the face of the mounting threat of Islamic conquest. Manuel was also one of many emperors who were unsuccessful in persuading western Christians to aid the fading empire. The pressing question is not only whether Islam will take up Benedict’s challenge but whether well-meaning Christians, who have sometimes wanted to feel removed from the battle, draw strength from the pope’s leadership.