The pope's staff and Vatican officials serenaded him with a birthday song over breakfast, Vatican Radio reported.
With Christmas eight days away, Francis preached on the presence of God in human lives from Abraham and Isaac to Jesus Christ.
"God has always walked alongside his people," the pope said.
Those present included Archbishop Pietro Parolin, the Vatican secretary of state, Cardinal Angelo Sodano, dean of the College of Cardinals, and Monsignor Konrad Krajewski, the papal almoner, who brought four homeless men who spend their time on the streets of Rome around Vatican City.
The staff of the Santa Marta guesthouse, where Francis has chosen to live instead of in the papal residence, also attended.
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