ROME -- Pope Francis is encouraging people to be joyful, saying, "We've never heard of a sad saint."

Some 50,000 people flocked to St. Peter's Square for the pope's traditional Sunday noontime window appearance. Among them were many children clutching figurines of baby Jesus for Francis to bless for Christmas creche scenes at home or school.

Francis said: "Man's heart desires joy. Every family, every people, aspires to happiness."

He said being "missionaries of joy" should be part of lifestyles to help people through difficulties. Holding up a pocket-sized prayer book, he urged the crowd to take free copies being distributed in the square

To symbolize joy in anticipation of Christmas, priests worldwide donned rose-colored vestments, just as the pope did Sunday evening for a Mass he celebrated at a parish in a working-class neighbourhood on Rome's outskirts.

During his homily, Francis said that this Sunday is known as the "Sunday of joy" in the Catholic church.

Many people in the rush toward Christmas fret about "all they still haven't" done for holiday preparations, he said. But, Francis said: "Think of all the good things life has given you."

"It hurts to see Christians with a bitter face, restless with bitterness because they are not at peace," he said. "Saints have the face of joy."

"Don't forget: 'joy,"' Francis said, just before leaving and gave a thumbs-up sign of appreciation to the parish musicians.

Greeting Francis when he arrived at church was a handmade sign proclaiming in Italian, "Happy Birthday, Holiness" in brightly colored letters. Francis turns 78 on Wednesday. The pope told the parents of 60 infants who were baptized in the parish during 2014 that his own baptism took place on Christmas Day in 1936.