Popes generally use their Easter Urbi et Orbi address, “to the city and the world,” to pray for peace amid global conflicts. Francis followed that tradition on Sunday, among other things commenting on a tentative nuclear deal between the P5+1 nations, including the United States, and Iran.

The pontiff said, “In hope we entrust to the merciful Lord the framework recently agreed to in Lausanne, that it may be a definitive step toward a more secure and fraternal world.”

That may not amount to a direct endorsement, but it’s certainly more favorable than the commentary coming from Israeli Prime Minister Benjamin Netanyahu or Republicans in Congress about the outline for an accord reached April 2 in Switzerland, not to mention Iranian hardliners who see it as a threat to their national interests. (On Monday, Israel backed off its insistence that Iran halt all uranium enrichment, a move seen as acknowledgement that the pact required concessions on all sides.)

US President Barack Obama could have problems mustering legislative support for a deal, in part because Republicans may want to make an issue out of it in 2016. At the same time, Iran’s Supreme Leader Ayatollah Ali Khamenei hasn’t yet explicitly embraced the agreement, and a political movement called “We Are Anxious,” founded last year to oppose nuclear concessions, is campaigning against it.

The Associated Press reported that roughly 200 hardliners rallied in front of the Iranian parliament building on Tuesday during hearings on the agreement, brandishing banners calling it a “defeat.”

Moderates on both sides of the divide, in other words, may struggle to bring along the hawks in their own shops. In that effort, the Vatican could turn out to be a surprisingly potent resource.

First of all, Pope Francis has plenty of political capital at the moment because of his high approval ratings and perceptions of his moral authority. He also has a proven capacity to translate that capital into results, as his role in restoring relations between the United States and Cuba illustrates.

If Francis were to lend his seal of approval to the nuclear deal, even campaigning for it in the oblique but unmistakable way popes sometimes do on political matters, it could move the needle in terms of public opinion.

On a more long-term basis, the Vatican may be the global institution with the best shot at rebuilding trust between Iran and the West.

Iran is a pervasively religious society whose ultimate authority is a cleric, and to get to the heart of things, one has to be able to engage them not just in terms of realpolitik, but also spiritual concepts. No Western statesman can do that credibly, but the Vatican can.

Moreover, there’s a natural affinity between Catholicism and Shi’a Islam, which is the minority branch of the Muslim world, but the culture-shaping majority in Iran.

Iranian writer Vali Nasr, author of the 2006 book, “The Shia Revival,” argues that the divide between Sunni and Shi’a bears comparison to that between Protestants and Catholics, with Shi’a being the branch closer to Catholicism.

Among the features of Shi’a Islam that parallel Catholicism are:

  • A strong emphasis on clerical authority
  • An approach to the Qur’an accenting both scripture and tradition
  • A deep mystical streak
  • Devotion to a holy family (in the case of Shi’ites, the blood relatives of Muhammad) and to saints (the Twelve Imams)
  • A theology of sacrifice and atonement through Hussein, who married the daughter of Muhammad and led the early Shi’a community, and is venerated for his death in the battle of Karbala
  • Belief in free will (as opposed to the Sunni doctrine of pre-destination)
  • Holy days, pilgrimages, and healing shrines
  • Intercessory prayer
  • Strongly emotional forms of popular devotion

As Nasr points out, anyone who’s ever watched a Good Friday procession in, say, Mexico or the Philippines, including people who flagellate themselves and even have themselves nailed to crosses to recall Christ’s crucifixion, will be struck by the eerie similarities with the Shi’a festival of Ashoura commemorating Hussein’s martyrdom.

Fellow Iranian writer Reza Aslan says that rational interpretation of Islamic law by Shi’ite clergy creates a flexibility sometimes lacking in Sunni Islam, which is often shackled to a literal reading of the Qur’an. Aslan believes Shi’a-influenced societies may be more amenable to experimentation with democracy, human rights, and pluralism, provided they’re grounded in religious reasoning — just as in Catholic social theory.

Benedictine Rev. Mark Serna, a veteran of Catholic/Islamic exchange, has written that “in distinction to Muslims in the Sunni tradition, Shi’ite Muslims are very natural dialogue partners with Roman Catholics.”

This isn’t to say the Vatican is uncritical in its approach to Iran. Above all, Pope Francis has become increasingly outspoken about anti-Christian violence, and Iran’s ambiguous relationship with radical forces that often target Christians and other minorities is a source of burning concern.

Yet the Vatican nonetheless favors keeping lines of communication open, and the interest is clearly reciprocated by Tehran. Diplomatic relations between Iran and the Holy See date to 1954, making them 30 years older than US/Vatican ties, and the Iranian embassy to the Holy See is well-known in Rome for its large staff and activist spirit.

When Vatican and Iranian officials sit down, they speak a common language shaped by shared spiritual and theological concepts.

In a small but telling sign, Italian Archbishop Vincenzo Paglia, who heads the Vatican’s Pontifical Council for the Family, recently met with a delegation of high-level Iranian women including Shahindokht Molaverdi, vice-president for women and family affairs. When the Iranians floated the idea of attending the upcoming World Meeting of Families in Philadelphia in September, an event Pope Francis will attend, Paglia immediately embraced it.

As a result, when Francis visits the United States, he’s set to bring an Iranian delegation in his wake. Not many world leaders could wrap such a gesture into their American debut without triggering a diplomatic fracas.

(Molaverdi told Crux in February she believes Francis could play a role in opening doors. “Certainly this pope has an ability to bring people together, which can also influence governments,” she said.)

Whether opportunities for dialogue can be mobilized quickly enough to make a difference over the nuclear pact, which is supposed to be finalized by June 30, remains to be seen.

Over time, however, if Iran and the West are to find common ground, Pope Francis and his Vatican team could be a key ingredient in making it happen.