Pope Francis leaves the Vatican on Saturday to pursue two kinds of peace: to meet with political and religious leaders in the bloodstained Middle East and also to embrace his own estranged Christian brother, Bartholomew, the ecumenical patriarch of Eastern Orthodoxy.

In Jordan and the occupied West Bank, Francis will meet refugees from conflicts, and he will celebrate Mass in Bethlehem, where the Christian Bible says Jesus was born. He also will meet privately with political leaders in the region, including Palestinian President Mahmoud Abbas and Israeli Prime Minister Benjamin Netanyahu.

His three-day visit comes as the U.S. tries to restart Middle East peace talks, which collapsed last month after Israel pulled out. Israel said it could not negotiate with a new Palestinian unity government that included Hamas, which Israel regards as a terrorist organization.

The Vatican has not revealed the specific talking points Francis wants to pursue with Abbas and Netanyahu, and Francis said this week his journey “is purely a religious trip.”

Odds against the success of the peace mission would seem to be all but overwhelming.

“The notion that he’s going to go and make a significant dent in this problem is delusional. Can he do anything? The answer is 100 percent no,” said Aaron David Miller, a former Middle East adviser to Republican and Democratic secretaries of state. “We need a miracle. If he can provide that, that’s the only way.”

The persecution of Christians in the Middle East also may be a topic of discussion.

Christian minorities in Jordan, the West Bank and Israel are not under intense assault. But in Egypt, Syria and Iraq, government pressure and mob violence have stirred fears that the centuries-old Christian presence in those lands may simply disappear.

The pope’s schedule is a study in balance. His presence on the West Bank and his visits with refugees there will focus world attention on their plight. But he also will visit the Yad Vashem Holocaust memorial and lay a wreath at the grave of Theodor Herzl, the founder of Zionism.

On the spiritual side, Francis will meet and pray with Bartholomew, the ecumenical patriarch and spiritual head of 300 million Orthodox Christians, who have followed a separate path since the churches of Rome and what was then Constantinople split nearly 1,000 years ago.

Francis will meet local Jewish and Muslim leaders in Jerusalem. And to underscore the theme of religious and political reconciliation, the Vatican said, he has invited an Argentinian rabbi and a Muslim religious leader, both old friends from his days as archbishop of Buenos Aires, to join him in Jerusalem.

Bartholomew’s companions will likewise include a friend, Muhtar Kent, the Turkish-American chairman of Coca-Cola, who is a Muslim, his office said.

Israel has imposed heavy security for the trip. It reportedly enlarged the security zone around Francis after he insisted that he ride in an open car.

A few acts of vandalism against Christian sites in Jerusalem have occurred in recent weeks, attributed to a small number of far-right vigilantes.

Praying together

Assuming there are no breakthrough announcements on the political front, the scheduled high point of the trip will come Sunday, when Francis and Bartholomew pray together at Jerusalem’s Church of the Holy Sepulcher, the traditional site of Jesus’ crucifixion and resurrection.

As ecumenical patriarch, Bartholomew is regarded by the patriarchs of 14 or 15 Eastern Orthodox churches as “first among equals.”

His jurisdiction includes the Greek Orthodox Church, among others, including its congregation at Holy Trinity Cathedral in New Orleans, the oldest Greek Orthodox congregation in the Western Hemisphere.

There are about 59 million Roman Catholics and 1 million Orthodox Christians in various denominations in the United States, according to the Association of Religion Data Archives.

About 2,500 Orthodox worship at eight congregations in Louisiana, compared with 1.2 million Louisiana Catholics.

The Jerusalem trip was born at Francis’ installation last year, when Bartholomew — viewed by the Orthodox faithful as the successor to the apostle St. Andrew, based in what is now Istanbul — invited Francis, viewed by Catholics as the successor to St. Peter based in Rome, to recommit their churches to healing an ancient breach.

He proposed that they meet in Jerusalem, sacred ground for both.

Francis accepted, and he added stops in Jordan and the West Bank to pursue political and humanitarian goals on the same trip.

The meeting between Francis and Bartholomew features two Christian leaders whose estranged communities have been slowly healing from the ancient, bitter separation.

After centuries of rising tension, Christianity finally broke apart in 1054. The reasons included abstract theological differences involving issues like the understanding of the Holy Spirit and practical disagreements over the extent of the Western pope’s authority over worldwide Christianity.

After the breach, the rival primates hurled mutual excommunications at each other. For nearly 1,000 years, the two churches did not talk, on any level.

Breakthrough moment

This weekend’s meetings between Francis and Bartholomew will mark the 50th anniversary of the breakthrough moment in 1964, when their predecessors, Pope Paul VI and Patriarch Athenagoras, met and resolved to begin a healing process.

Even after 50 years, though, observers caution against expecting any new announcements.

“This kind of work goes centimeter by centimeter,” said New Orleans Archbishop Gregory Aymond who, with other American Catholic bishops and theologians, served on a standing commission exploring differences with Orthodox counterparts.

“People don’t realize how bad things were before,” said the Rev. Ron Roberson, who works on ecumenism with the U.S. Conference of Catholic Bishops. “Before 1964, there had been no communication whatsoever between the two for hundreds of years. Not bad relations — I mean no relations. Since then, there’s been a tremendous improvement in communications.”

Before then, Orthodox Christians and Roman Catholics could not worship together, could not intermarry in each other’s churches and could not take the Eucharist together.

On a theological level, according to Roberson, in Western Catholicism, the Holy Spirit is seen at work in the church through individual officeholders, like the pope, who are invested with authority to teach and protect the faith. In Orthodoxy, authority is more communal and is more commonly found in consensus. Also, governance is more diffuse in the Orthodox world. The Eastern patriarch does not have the authority in his world that the pope does in the West.

Moreover, some Orthodox churches are less interested in unity than others, Roberson said. Russian and some other Orthodox churches spent generations under communist persecution. “Persecution breeds conservatism, and that means hanging onto the faith as you know it,” he said.

“Bartholomew can’t get ahead of his wide flock, because a lot of those churches are not ready for this. He has to be careful of the extent to which he can speak for Orthodoxy as a whole.”

Differences on sacraments

In the U.S., after 45 years of dialogue between American Catholics and Orthodox representatives, the Catholic Church recognizes all the Orthodox sacraments, Roberson said. But the reverse is not true.

Greek Orthodoxy, the largest U.S. Orthodox community, does not recognize Catholic weddings, so as a practical matter, “99 percent of mixed marriages between a Roman Catholic and someone who is Greek Orthodox take place in an Orthodox church, which will recognize the marriage for both,” said the Rev. Dean Gigicos, the interim pastor of Holy Trinity in New Orleans.

And there are still larger disagreements.

“The root obstacle preventing the Orthodox and Catholic churches from growing steadily toward sacramental and practical unity has been, and continues to be, the role that the bishop of Rome plays in the worldwide Catholic communion,” a joint committee wrote in 2010.

That difference means that, despite other kinds of progress, Catholics and Orthodox still may not take each other’s Eucharist.

In his papacy of less than two years, Francis has demonstrated a taste for cutting against the grain of Catholic convention and producing surprises. Still, Aymond cautions against expecting big news this weekend.

“As pope, he can do and say almost anything,” Aymond said. “But I would think this issue is so historic and so complicated — not here. There would have to be some consultation with the College of Cardinals and the bishops of the world, and I don’t think there has been.”

Like Aymond, Gigicos said he expects something more modest, such as a recommitment to continue the slow healing work already underway.

“This will be a reaffirmation of success of that first meeting (in 1964) and a pledge to continue dialogue with the promise that the church will be one again,” he said.