Pope Francis says the Roman Catholic Church must strip itself of all "vanity, arrogance and pride" and humbly serve the poorest in society.
Francis hosted a lunch for the poor in the town of Assisi, the birthplace of his namesake, a 13th Century saint.
"Many of you have been stripped by this savage world," he said. "[It] does not give employment [and it] does not care if there are children dying of hunger."
The pontiff has been in talks about a programme of reform for the Vatican.
He has said he wants today's Catholic Church to resemble Francis of Assisi's "Church of the poor".
The Pope arrived to cheering crowds and later spoke to guests at a lunch in the Caritas reception centre.
Francis was visibly moved when he heard the stories of some of the poor people in the room.
"[The world] does not care if so many families have nothing to eat," he said.
Thousands of people gathered for Mass in front of the Basilica of Saint Francis.
"Today is a day for crying," Francis said, referring to the hundreds of deaths feared in the sinking of a migrant boat off the island of Lampedusa.
He said the world "did not care about those fleeing poverty and hunger, who seek freedom but instead find death".
One of those in the congregation, Irene Lunghi, described it as "a serious ceremony, simple and also a bit humble, like St Francis himself".
Another member of the audience, Father Dionysus Mintov, said the sinking off Lampedusa was a "terrible tragedy". "The Mediterranean has become a big cemetery," he said. "Men like us, who suffer, they are poor."
The Pope has suggested empty buildings of monastic orders could be used as accommodation for migrants and refugees.
Speaking in a hall where St Francis was said to have thrown off his robes in a gesture of humility, the Pope called on the Catholic Church and its followers to rid themselves of earthly concerns.
"The Church, all of us should divest ourselves of worldliness. Worldliness is a murderer because it kills souls, kills people, kills the Church."
"Without divesting ourselves, we would become pastry-shop Christians, like beautiful cakes and sweet things but not real Christians," he said.
Two days ago Pope Francis told Italian newspaper La Repubblica his namesake had "longed for a poor Church that looked after others, accepted monetary help and used it to help others with no thought of itself".
"Eight hundred years have passed and times have changed, but the ideal of a missionary and poor Church is still more than valid," he said.
Known in Italian as Il Poverello, or the Poor One, St Francis was the son of a wealthy local cloth merchant who scandalised his family when he reached the age of 25 by dumping his expensive clothing and living in sackcloth, ministering to the poor for the rest of his life.
Pope Francis has become known for his candid views - unlike anything heard coming out of the Vatican during recent papacies, says the BBC's David Willey in Rome.
He wants to see an overhaul of the Church, bringing it closer to ordinary people.