The unidentified man doused himself with gasoline he carried in a bottle then lit himself aflame at the end of the colonnade near Piazza Pio XII.
Pope Francis said Christmas is an occasion of joy but also a lesson in humility, when the faithful are called to imitate the example of God-made-man.
The pope made his remarks Wednesday during his weekly public audience in St. Peter's Square.
"God abases himself, descends to earth as someone small and poor, which means that to be like him we should not put ourselves above others, but on the contrary, abase ourselves, give ourselves in service, make ourselves small with the small and poor with the poor," he said.
To celebrate his 77th birthday, Pope Francis celebrated Mass and had breakfast with three people who live on the streets near the Vatican.
When Pope Francis announced in April that he would convene a sort of "kitchen cabinet" of the world's cardinals, he gave the group two general objectives: to help him in reforming the Vatican's bureaucracy and to advise him in governing the global church.
While we are still waiting to see exactly where pursuit of the first goal will lead, December's meeting of the Council of Cardinals saw the group embracing the second.
The trafficking of human beings is a crime against humanity and must be stopped, Pope Francis told diplomats.
"It's a disgrace" that people are treated "as objects, deceived, raped, often sold many times for different purposes and, in the end, killed or, in any case, physically and mentally damaged, ending up thrown away and abandoned," he said.
An official at the Pontifical Council for Justice and Peace said despite widespread news reports, he does not expect Pope Francis to write an encyclical on poverty.
"The consultation must gather information from the grass roots and not limit itself to the level of the Curia or other institutions," said Archbishop Lorenzo Baldisseri.
All people must stand united against the scandal of hunger while avoiding food waste and irresponsible use of the world's resources, Pope Francis said Monday.
People should "stop thinking that our daily actions do not have an impact on the lives of those who suffer from hunger firsthand," the pope said, as he launched a global campaign of prayer and action against hunger.
Pope Francis advanced the sainthood causes of 13 candidates, including the "father of Puerto Rican public education" and the Canadian founder of a religious order dedicated to helping unwed mothers.
During a meeting Monday with Cardinal Angelo Amato, prefect of the Congregation for Saints' Causes, the pope signed decrees recognizing that Rafael Cordero Molino and Mother Rosalie Cadron-Jette lived the Christian virtues in a heroic way and are venerable.
People can say things that sound Christian and call themselves Christian as they tell others what to do, but if they don't pray often and live the Gospel, they harm others and the church, Pope Francis said.
Concelebrating his morning Mass on Thursday with the eight members of the Council of Cardinals advising him on the reform of the Roman Curia and church governance, Pope Francis prayed that God would give all Christians "the grace of humility" to build their lives on the rock that is Christ.