This is one of the desires St. Paul had for his people in Rome, when he wrote "may the God of hope fill you with joy," Pope Francis explained.
He noted that the expression "full of joy" continues to be repeated throughout the Acts of the Apostles and on the day of Jesus' ascension.
"The disciples returned to Jerusalem, says the Bible, 'full of joy.'"
Pope Francis encouraged people to read the last few paragraphs of St. Pope Paul VI's exhortation, Evangelii nuntiandi.
Pope Paul VI "speaks of joyful Christians, joyful evangelizers, and not those who live always 'down,'" Francis said.
He also pointed to a passage in the Book of Nehemiah which he said can help Catholics reflect on joy.
In Nehemiah chapter 8, the people returned to Jerusalem and rediscovered the book of the law. There was a "great celebration and all the people gathered to listen to the priest Ezra, who read the book of the law," the pope described.
The people were moved and wept tears of joy, he said. "When the priest Ezra finished, Nehemiah said to the people: 'Rest assured, now do not cry anymore, keep the joy, because joy in the Lord is your strength.'"
Pope Francis said, "this word from the book of Nehemiah will help us today."
"The great strength that we have to transform, to preach the Gospel, to go forward as witnesses of life is the joy of the Lord, which is a fruit of the Holy Spirit, and today we ask him to grant us this fruit," he concluded.
At the end of Mass, Pope Francis led an act of spiritual communion for all those who cannot receive the Eucharist and offered several minutes of silent adoration concluding with benediction.
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Francis' intention during the Mass, offered amid the coronavirus pandemic, was for pharmacists: "they too work a lot to help the sick recover from sickness," he said. "We also pray for them."
Hannah Brockhaus is Catholic News Agency's senior Rome correspondent. She grew up in Omaha, Nebraska, and has a degree in English from Truman State University in Missouri.