The Pope has appealed for prayers for his visit to Cuba and the US, which begins on Saturday.
The Vatican revealed that he is still not comfortable speaking English and will use his native Spanish to deliver all but four of his 18 addresses.
At the end of today's general audience in Rome, Pope Francis said he is going "with great hope".
The main reason for the visit is to address the World Meeting of Families in Philadelphia, Pennsylvania. He will also visit the headquarters of the United Nations on its 70th anniversary, visit Washington and meet President Barack Obama.
"Even now I greet with affection the Cuban and American people, who, guided by their pastors, are spiritually prepared. I ask everyone to accompany me with prayer, invoking the light and strength of the Holy Spirit and the intercession of Mary Most Holy, Patroness of Cuba as the Virgin of Charity of Cobre, and Patroness of the United States of America as the Immaculate Conception," he said.
He might also meet Fidel Castro in Cuba although this depends on the former president's health, which is frail.
Pope Francis, aged 78, was expected to start using more English. He has been practising the language over the summer. But he has stated his wish to stick mainly with Spanish, in which he can be more free with his immediate, colloquial style his passionate appeals to congregations. Spanish is the second most used language in the US which has a Hispanic community of about 54 million, 17 per cent of the population.
At a Vatican briefing on the visit, a spokesman said: "He feels more comfortable with Spanish. The real reason is the ease of expression and that he will have to make less effort."
He will use English for his speech at the official welcoming ceremony at the White House and when he addresses the US Congress.
Additional reporting by Reuters