The pontiff, at his annual Christmas Eve Mass at Saint Peter's Basilica, called on Christians everywhere to push back against the excesses of modern society, which he said was "so often intoxicated by consumerism and hedonism, wealth and extravagance, appearances and narcissism".
Christianity calls on believers "to act soberly -- in other words, in a way that is simple, balanced, consistent, capable of seeing and doing what is essential," said the 79-year old pope, leader of the world's 1.2 billion Catholics.
"In a world which all too often is merciless to the sinner and lenient to the sin, we need to cultivate a strong sense of justice, to discern and to do God's will," the Argentine pontiff said.
Condemning a "culture of indifference which not infrequently turns ruthless", the pope asked Catholics to combine prayer with an attitude of "empathy, compassion and mercy" after a year of global unrest that saw one million migrants and refugees, mostly from Syria, reach Europe in search of a better life.
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Half a world away in Bethlehem, the head of the Roman Catholic Church in the Holy Land arrived for the traditional midnight mass at the Church of the Nativity -- built over the site where Christians believe Jesus was born.
Travelling from Jerusalem nearby, the Jordanian Latin patriarch Fouad Twal would have had to pass through the Israeli wall that separates the two cities, with Bethlehem located in the occupied West Bank.
Violent protests and a series of Palestinian attacks on Israelis since October have killed 129 Palestinians, 19 Israelis, an American and an Eritrean. Many of the Palestinians were attackers, while others were killed in clashes.
The Bethlehem mass commemorating the birth of Jesus will be dedicated to victims of violence and their families, Twal said, with celebrations "moderate" due to violence in the Palestinian territories, Israel and the world.