Before celebrating an outdoor Mass, Francis led a procession through St Peter's Square to usher in Holy Week, the solemn period leading to Easter. Faithful Catholics clutching olive branches and braided palm fronds received his blessing.
Francis abandoned his homily text to lament Europe's handling of the influx of migrants and asylum-seekers fleeing war, persecution or poverty from Syria, Iraq, Africa and elsewhere.
Palm Sunday recalls a crowd's triumphant welcome of Jesus entering Jerusalem. But soon Jesus would be condemned to be crucified after a series of authorities declined to rule on his fate.
Jesus was "denied every justice," the pope said. "Jesus also suffered on his own skin indifference, because no one wanted to take on the responsibility for his destiny."
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"And I am thinking of so many people, so many on the margins, so many refugees" for whom "many don't want to assume responsibility for their destiny," Francis said in a clear reference to Europe's migration debate.
After the Mass, Francis joyfully greeted tens of thousands of people as he toured the square in his white popemobile, and let some children aboard for a while.