Francis' comments came Friday during a lunch he hosted for poor in Assisi, the BBC reported.
"The Church, all of us should divest ourselves of worldliness. Worldliness is a murderer because it kills souls, kills people, kills the Church," Francis said. "Without divesting ourselves, we would become pastry-shop Christians, like beautiful cakes and sweet things but not real Christians."
During his trip, Francis said many priests' sermons are boring, Italy's ANSA news agency reported.
"These (kinds of) homilies -- [are] endless, tedious, in which you do not understand anything," Francis said at a meeting with clergy members at the Cathedral of San Rufino.
The pope called on nuns to smile more genuinely, ANSA said.
"I am so disappointed when I encounter nuns who are joyless, who may smile with the smile of a flight attendant but not with the smile of joy that comes from within," told nuns at the Santa Chiara cloistered convent.
"Love one other, for the monastery must not be a purgatory but rather a family. There are and will be problems and they will be solved as in a family: With love," he said.