The Vatican said a record number of people had applied to attend the mass, CNN reported.
"On this night, let us share the joy of the Gospel. God loves us. He so loves us that he gave us his son to be our brother, to be light in our darkness. To us the Lord repeats, 'Do not be afraid,' ... And I, too, repeat, do not be afraid,'" Francis told the congregation packed into the basilica.
Francis succeeded Pope Benedict XVI in March. Benedict, the first pope to retire in several hundred years, is still living in Vatican City, and Francis paid him a Christmas visit as well as spending 3 hours in a children's hospital.
The new pope has a different style from his predecessors, choosing to live in a Vatican guest house instead of in the papal palace. Francis, the first non-European pope in more than a thousand years, is also the first Jesuit and the first to take the name of one of the Catholic Church's most popular saints.
"People are listening to him, because he's speaking in a language that's not Vaticanese," Gerald O'Connell, a Vatican observer, told CNN. "He's speaking the language of ordinary people."
On Christmas Day, the pope is scheduled to deliver his first Christmas message to the throngs expected in St. Peter's Square.
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