Francis' last message to America: Don't be afraid of new things!

Pope Francis ended his exhaustive six-day, three-city tour of the U.S. Sunday with a strong exhortation to American Catholics to be unafraid of trying new things, even if they seem to threaten long-practiced traditions or existing church structures.

In a homily to hundreds of thousands at an outdoor Mass packing Philadelphia's iconic Benjamin Franklin Parkway, Francis said that Jesus' disciples were also afraid of new things -- but that Jesus broke down all barriers to allow the Spirit to do its work.

"Jesus encountered hostility from people who did not accept what he said and did," the pope told the crowds, many of whom had waited for long hours to participate in the last of his three public Masses while in the U.S.

"For them, his openness to the honest and sincere faith of many men and women who were not part of God’s chosen people seemed intolerable," said the pontiff.

"The disciples, for their part, acted in good faith," he said. "But the temptation to be scandalized by the freedom of God, who sends rain on the righteous and the unrighteous alike, bypassing bureaucracy, officialdom and inner circles, threatens the authenticity of faith. Hence it must be vigorously rejected."

"For Jesus, the truly 'intolerable' scandal consists in everything that breaks down and destroys our trust in the working of the Spirit!" said Francis.

God, the pope said, "will not be outdone in generosity and he continues to scatter seeds."

"He scatters the seeds of his presence in our world, for 'love consists in this, not that we have loved God but that he loved us' first," said the pontiff. "That love gives us a profound certainty: We are sought by God; he waits for us."

"It is this confidence that makes disciples encourage, support and nurture the good things happening all around them," said Francis. "To raise doubts about the working of the Spirit, to give the impression that it cannot take place in those who are not 'part of our group,' who are not 'like us,' is a dangerous temptation."

"Not only does it block conversion to the faith; it is a perversion of faith!" he said.

Francis was speaking Sunday in a Mass that had attracted an incredible number of people to Philadelphia's downtown area. On the way to the ceremony, the pope greeted people from the pope-mobile, struggling to make its way through the densely packed crowds.

The pontiff stopped the vehicle dozens of times, pointing at and calling forth babies to bless and kiss.

Security for Francis' visit to Philadelphia has been extraordinary. The downtown area has essentially been shut down for a several mile radius, with all vehicle traffic barred and people forced to go on foot through airport-style security checkpoints.

Uniformed police and military have been patrolling streets, crowds, and local stores -- sometimes outnumbering pilgrims.

The security measures caused issues for many planning to attend the Mass, who endured mile-long lines to enter the security checkpoints but were unable to be cleared in time. One group from New Jersey had entered the line at 10 a.m. for the 4 p.m. Mass but was eventually forced to give up.

Francis' homily Sunday was the last in a series of powerful speeches he has made on his U.S. trip, directed at a wide range of constituencies. He has been in the U.S. since Tuesday, visiting the cities of Washington, New York, and Philadelphia.

In Washington, he spoke to President Barack Obama, Congress and political leaders, and the U.S. bishops; in New York to the United Nations; in Philadelphia to lay people and a group of international bishops.

In Sunday's homily, Francis reflected on a Gospel reading that sees the disciples ask Jesus whether they should rebuke others who are healing in his name. Jesus replies: "There is no one who performs a mighty deed in my name who can at the same time speak ill of me."

The pope said that just like happiness, holiness is "tied to little gestures."

"These little gestures are those we learn at home, in the family; they get lost amid all the other things we do, yet they do make each day different," he said. "They are the quiet things done by mothers and grandmothers, by fathers and grandfathers, by children."

"Love is shown by little things, by attention to small daily signs which make us feel at home. Faith grows when it is lived and shaped by love," said the pope. "That is why our families, our homes, are true domestic churches. They are the right place for faith to become life, and life to become faith."

Commenting on how many had gathered for the Mass, Francis said: "This is itself something prophetic, a kind of miracle in today’s world."

"Would that we could all be prophets!" he said. "Would that all of us could be open to miracles of love for the sake of all the families of the world, and thus overcome the scandal of a narrow, petty love, closed in on itself, impatient of others!"

The pontiff then offered an expansive gesture of gratitude to all families.

"Anyone who wants to bring into this world a family which teaches children to be excited by every gesture aimed at overcoming evil -- a family which shows that the Spirit is alive and at work -- will encounter our gratitude and our appreciation," said Francis. "Whatever the family, people, region, or religion to which they belong!"

Francis heads back to Rome Sunday evening, after one last short meeting with some 500 members of the World Meeting of Families, a Vatican sponsored every three-year event that was held in Philadelphia last week.

The pontiff will be sent off from Philadelphia by Vice President Joe Biden and his wife Jill, who have traveled from Washington to offer a formal goodbye to the pope from the country.

[Joshua J. McElwee is an NCR Vatican correspondent. His email address is jmcelwee@ncronline.org. Follow him on Twitter: @joshjmac.]