Pope Benedict urged Cubans to build a better, renewed and open society on Monday and pressed the communist government to give the Catholic Church more liberties to help the country as it faced an uncertain future.
Arriving from Mexico to start his first trip to Cuba, the pope also called for a future of freedom and reconciliation in Cuba.
Benedict celebrated an open-air Mass for tens of thousands of people Revolution Square ringed by palm trees in this eastern city, and he delivered a strong, clear message in his sermon as President Raul Castro listened from the front row.
I appeal to you to reinvigorate your faith, that you live in Christ and for Christ, and armed with peace, forgiveness and understanding, that you may strive to build a renewed and open society, a better society, one more worthy of humanity, and which better reflects the goodness of God, he said.
At the start of the Mass, a man shouting Down with communism was taken away by security officials. Others in the crowded booed the man for spoiling the atmosphere and shouted Cuba, Cuba, Cuba.
Just three days after saying that communism no longer works in Cuba, the 84-year-old German pope took a somewhat softer stance as he began a three-day trip aimed at boosting the Church's role on the island.
Arriving in the city of Santiago de Cuba, he delivered a carefully worded, nuanced and balanced speech that was less direct in criticizing Cuba's one-party system but included some thinly-veiled phrases addressing its human rights record.
I carry in my heart the just aspirations and legitimate desires of all Cubans, wherever they may be, he said, including the sufferings of prisoners and their families, a reference likely to be well received by political dissidents on the island as well as Cuban American exiles in the United States.
He also asked the Virgin of Charity of El Cobre, Cuba's patron, to guide the future of this beloved nation in the ways of justice, peace, freedom and reconciliation.
Decades of hostility followed Cuba's 1959 revolution but Church-state relations have improved steadily in recent years, helped by Pope John Paul II's landmark visit in 1998.
Benedict called that trip a gentle breath of fresh air but said that while great strides had been made, many areas remain in which greater progress can and ought to be made, especially as regards the indispensable public contribution that religion is called to make in the life of society.
Cuban bishops and the government are still at odds over issues such as Church use of the media and public education, which the Church considers are fundamental to its role as a moral force in society.
Benedict is trying to cement the Church's recent gains here and offer more help in assuring that whatever transition comes is buffered by its social programs, such as care centres for the elderly and limited after-school and adult education programs.
Castro, younger brother of Cuba's revolutionary leader Fidel, warmly greeted the pope at the airport, grasping both of his hands and briefly bowing before him.
The president, who was raised a Catholic, was dressed in a dark suit and was accompanied by a full Honour Guard and artillery gun salute for the pope. When the wind blew Benedict's white vestments around his head, Castro put them back across his shoulders.
He then delivered a firm political lecture about the injustices of U.S. hostility toward Cuba, including a 50-year-old economic embargo, and the island's tenacious resistance to preserve its independence and follow its own path.
Castro has steadily improved relations with the Church using it as an interlocutor on issues such as political prisoners and dissidents, while moving forward with reforms to Cuba's struggling Soviet-style economy.
They include slashing a million government jobs and freeing up some sectors to small-scale private enterprise. The Church has urged Castro to move farther and faster to modernize Cuba, both economically and politically.
Benedict fired an unexpected salvo on Friday when he told reporters on his plane that communism in Cuba had failed and a new economic model was needed, adding that the Church was willing to offer its help to avoid traumas.
The Cuban government offered a diplomatic response to the Pope's criticism, saying that Cuba would listen with all respect to the Pope and welcomed the exchange of ideas.
In what appeared to be an effort to balance his remarks, Benedict made an apparent dig at capitalist greed on Monday, blaming the global economic crisis on the ambition and selfishness of certain powers which take little account of the true good of individuals and families.
Cuba is going through a key moment in its history, Benedict said, hinting that with the advancing age of the Castro brothers the island was already looking to the future.
Church officials say Benedict's schedule in Cuba has not allowed for meetings with dissidents, who say Castro's government flouts human rights and suppresses their voices.
The dissident movement Damas de Blanco, or Ladies in White, a group of Catholic women that campaigns for the release of political prisoners, said it had been told by Cuban authorities to keep clear of the pope's Mass in Santiago.
They are going to present the pope with a facade, not with the true Cuba, said Ana Celia Rodriguez, a 42-year-old mother of three who is planning to try to attend anyway.
I really don't expect much change from the pope's visit. He'll see a Cuba that doesn't exist. My message for the pope is that he ought to see how things really are.
More than 70 members of the Ladies in White were detained briefly last week, fuelling concerns that the government, which views opponents as mercenaries of the United States, might clamp down to prevent public demonstrations during the pope's stay.
(Additional reporting by Jeff Franks and Nelson Acosta; Editing by David Adams and Kieran Murray)