Pope Francis strongly defended immigrants at his Christmas Eve Mass on Sunday, comparing them to Mary and Joseph finding no place to stay in Bethlehem and saying faith demands that foreigners be welcomed.

Francis, celebrating his fifth Christmas as leader of the world’s 1.2 billion Roman Catholics, led a solemn Mass for about 10,000 people in St. Peter’s Basilica while many others followed the service from the square outside.

Security was stepped up, with participants checked as they approached St. Peter’s Square even before going through metal detectors to enter the basilica. The square had been cleared out hours earlier so security procedures could be put in place.

Wearing white vestments in the flower-bedecked church, Francis called for a “new social imagination … in which none have to feel that there is no room for them on this earth.”

The 81-year-old pope, who was born of Italian immigrant stock in Argentina, has made defense of migrants a major plank of his papacy, often putting him at odds with politicians.