CASERTA, ITALY— Pope Francis traveled today to the southern Italian city of Caserta to meet some old Protestant friends and to pray with them, a trip that culminated with an apology from the pope for persecution of Christianity’s burgeoning Pentecostal movement by the Catholic Church.

“I ask for your forgiveness for those who, calling themselves Catholic, didn’t understand we’re brothers,” he said, receiving a standing ovation.

Francis also made a plug for greater unity among Christians, calling for “a church that is one in its diversity.”

“Pentecostal” is a term for Christians attracted to a high-octane style of praise and worship, who typically practice “gifts of the Holy Spirit” that include speaking in tongues as well as miraculous healings and deliverance from evil spirits. Born in the early 20th century, Pentecostalism today has a global following estimated at almost 300 million.

In some parts of the world, including the pontiff’s native Latin America, Pentecostal growth has come primarily at the expense of the Catholic Church, leading to tensions on both sides and occasional outbreaks of violence.

The pontiff’s host for the short outing to Caserta was an old friend from Argentina, an Italian Evangelical Pentecostal pastor named Giovanni Traettino. Francis had actually come down to Caserta the first time on Saturday to visit local Catholics, but his return on Monday brought him to a markedly different part of town.

Rather than stopping at the city’s imposing 18th-century Reggia palace, Monday saw Francis enter a new Evangelical church still under construction at the city’s outskirts, in a zone known as a mob stronghold.

The trip was part of a pattern of outreach from Francis to Evangelicals and Pentecostals, and a continuation of a commitment to Christian unity that began in Argentina.

Today’s encounter, originally presented by the Vatican as a personal visit to Traettino, was actually attended by 350 people. The guest list, chosen by the pastor himself, included Matteo Calisi, former president of the Catholic Charismatic movement, and Jorge Himitian, an Argentinian Protestant who first introduced the two leaders.

The pontiff arrived to the Evangelical Church of Reconciliation after a private visit to Traettino’s house. Traettino defined the visit as “a gesture that opened the door to reconciliation and answered to God’s request of being one church.”

“What we saw today is what we normally see in the outskirts of all major cities: a temple in the making, with only the structure of what, in the future, will be a big Pentecostal Church,” said Guillermo Ortiz of Vatican Radio.

Ortiz told the Globe that Traettino, the Protestant pastor, said to him that “many Evangelicals love Pope Francis. Some would even say that the Holy Spirit had something to do with his election.”

Traettino praised Francis by saying that the pontiff is not a man who delivers a message, “he lives it” when he approaches the ill, the poor and the lonely.

In his remarks, Francis described relations among Christians as an encounter between brothers who walk in the presence of God.

He said that the work of the Holy Spirit, regarded by Protestants and Catholics alike as the third person of the Holy Trinity, wants a church that doesn’t resemble a sphere but a polyhedron, meaning a complex structure built from several different things.

“He [the Holy Spirit] builds unity from diversity,” Francis said.

Since his election the pontiff has welcomed various leaders of Protestant organizations to the Vatican, including a June 24 encounter with members of the World Evangelical Alliance, the Communion of Evangelical Episcopal Churches, Kenneth Copeland Ministries from the United States, the global network Partners in Harvest and the missionary and relief organization Life Outreach International.

Francis and Traettino originally met through an Argentine movement called “Renewed Communion of Evangelicals and Catholics in the Spirit.” In 2006, the two men participated in a prayer service that drew 7,000 people to the Luna Park in Buenos Aires, a venue ordinarily used for boxing matches.

The future pope allowed himself to be prayed over on that occasion by a delegation of Protestant clergy, drawing fire from more conservative quarters in both the Protestant and Catholic worlds.

On the eve of his trip to Caserta, Francis got a fresh reminder of the obstacles to greater unity.

On Saturday, a group of Italian Protestant federation that claims to represent 80% of the country’s Evangelicals issued a declaration asserting that as long as the Catholic Church continues to promote positions “incompatible with the Scriptures”, such as its teachings on the Virgin Mary and the saints, the similarities some sectors of Catholicism share with Evangelical spirituality “aren’t a cause for hope for a real change in the church.”

“This is a pope who originally declared war on the Evangelical movements that have conquered many Latin American countries,” said Pastor Elpidio Pazzella of the Federation of Pentecostal Churches.

Pazzella said that the pope’s conversion to unity came only after “seeing the decrease in the faithful and religious vocations as a result of internationally renowned scandals,” and that Francis is now cynically “changing Rome’s strategy by pursuing alliances with other Christian denominations.”

Pope Francis himself offered a different version of how he changed his mind during a flight back from World Youth Day in Rio de Janeiro, Brazil, on July 28, 2013.

“Back at the end of the 1970s and the beginning of the 1980s, I had no time for charismatics,” the pope said. “Once, speaking about them, I said: ‘These people confuse a liturgical celebration with samba lessons.’”

“Now I regret it,” Francis said. “I think that this movement does much good for the church overall.”

According to a Pew Forum analysis done in 2011, there are today 279 million Pentecostal Christians and 305 million charismatics within established Christian denominations. Together, they make up over 25 percent of all Christians and almost 6 percent of the world’s population.

Himitian said today’s encounter should be seen as a visit from one friend to another, playing down expectations for an immediate breakthrough.

“We’ve learned from past experiences that the institutional road, even when based in theology, always becomes a dead end because it runs into the doctrinal and practical differences,” he said.

“The dialogue we have is based on friendship and spirituality,” he said.

Missing from today’s meeting was a British-born and South Africa-raised Protestant cleric named Bishop Tony Palmer of the Communion of Evangelical Episcopal Churches, who got to know the future pope in Argentina.

Back in January, Palmer visited Francis in the Vatican and used his cellphone to record a message that Francis addressed to a conference led by American Pentecostal Kenneth Copeland in which the pope offered a “spiritual hug.”

“God has begun the miracle of unity,” Francis said in his video, “God never begins a miracle he does not finish well.”

Palmer died unexpectedly July 20 in a motorcycle accident near Bath in the United Kingdom.

During remarks he made on Saturday in a Mass that drew more than 200,000 people to Caserta, Francis renewed his attack on organized crime and called for nature to be protected from abuse in a region scarred by toxic waste illegally dumped by the Camorra mafia.