Pope Francis underscored the importance of being joyful by contrasting sad Christian faces – which are more like "pickled peppers" – with the testimony of a beautiful life.

"Sometimes these melancholic Christians' faces have more in common with pickled peppers than the joy of having a beautiful life," Pope Francis said May 10.

"If we keep this joy to ourselves it will make us sick in the end, our hearts will grow old and wrinkled and our faces will no longer transmit that great joy, only nostalgia and melancholy which is not healthy," he added.

The Pope delivered his homily on the reading from Acts 18 in the chapel of St. Martha's residence.

He concelebrated the Mass with the Archbishop of Mérida, Baltazar Enrique Porras Cardozo, and the abbot primate of the Benedictine monks, Notker Wolf.

Vatican Radio staff and their director, Father Federico Lombardi, also attended the Eucharistic celebration.

The pontiff told them Christians should not keep joy "bottled up" for themselves because they risk becoming nostalgic.

Christian joy is not like "having fun, which is good," he explained, rather it "is more, it is something else."

"If we want to have fun all the time, in the end it becomes shallow, superficial, and also leads us to that state where we lack Christian wisdom, it makes us a little bit stupid, naive, no?" Pope Francis said.

"Joy is something that does not come from short term economic reasons, from momentary reasons, it is something deeper, it is a gift," he preached.

The pontiff described joy as "a gift from God" that "fills us from within" and "cannot be held at heel, it must be let go."  

"It is a virtue of the great, of those great ones who rise above the little things in life, above human pettiness," said Pope Francis.

He explained that it is a virtue "of those who will not allow themselves to be dragged into those little things within the community, within the Church" and that "they always look to the horizon."

He added that today's visit by Coptic Pope of Egypt Tawadros II was "a very good reason to be joyful because he is a brother who comes to visit the Church of Rome to speak and to walk part of the path together."