Pope Francis' trip to the United States in September will be a landmark event, with the first pontiff from Latin America expected to give some of the most important speeches of his papacy, church experts said Wednesday.

Francis is to arrive in late September for a five-day visit to New York, Philadelphia and Washington, D.C., after a recently announced trip to Cuba.

His addresses to Congress and the United Nations General Assembly could be "some of the greatest speeches of his pontificate," said Austen Ivereigh, author of "The Great Reformer: Francis and the Making of a Radical Pope."

Francis is "totally willing to cause offense" in the sense of challenging people, Ivereigh said. "He's totally devoid of political correctness. I think he will challenge almost everybody. He's a reformer, and he's a radical, and he's a change agent."

Ivereigh spoke Wednesday before about 300 people at the 24th annual World Communications Day Catholic Media Conference organized by the Diocese of Brooklyn. The theme was the pope's upcoming visit.

Francis has "given some very important speeches, but never on the platform and in the pulpits that he will have in the United States. It's a visit to the biggest platforms in the world," said David Gibson, a longtime Vatican reporter and author of "Finding Jesus: Faith. Fact. Forgery."

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This pope has never visited the United States and is "boning up" on the country, Ivereigh said. "He's talking to an enormous number of people."

Bishop Nicholas DiMarzio of the Diocese of Brooklyn said he expects to greet Francis when he lands at Kennedy Airport after first visiting Washington. The pope may visit St. Patrick's Cathedral that afternoon or evening, DiMarzio said, though the pontiff's schedule is still tentative.

The next morning he will address the United Nations, and in the afternoon possibly celebrate a Mass at Madison Square Garden, DiMarzio said.

Francis is expected to conclude his visit with a massive outdoor Mass on the Benjamin Franklin Parkway in Philadelphia, church officials said.

One challenge in covering the pope's visit will be his language, panelists said. Gibson said Francis' English "is not great" and he may switch to other languages, including his native Spanish.

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"It could be the best line of the day or the trip, and it could be in Spanish," Gibson said.

Joseph Zwilling, spokesman for the Archdiocese of New York, predicted that whatever languages the pope uses, the trip will be "a tremendous blessing for the church in New York, the church in the United States, and even for non-Catholics."