Pope Francis denounced the evil of consumerism Monday just as stores were offering discounts to online Christmas shoppers for “Cyber Monday.”

There is a disease against generosity, the pope told the faithful gathered for morning Mass in the Vatican, and it is called “the disease of consumerism.”

This disease, he said, leads people “to always buy things and to possess, but why? To have things just in case I need them.”

When I lived in Buenos Aires, the pope recalled, “every weekend there was a tourism shopping program: the plane would fill up on Friday evening and go off to some country — a flight of about ten hours — and then all day Saturday and part of Sunday in stores to buy and buy, and then return.”

“Today’s consumerism is a serious disease,” Francis said. “I am not saying that we all do this, but consumerism — buying more than we need, a lack of austerity in life — this is an enemy of generosity.”

As a practical exercise, the pontiff proposed, “taking a little trip through our room, through our closet. How many pairs of shoes do I have? One, two, three, four, fifteen, twenty? Each one can find the answer. A little too much.”

“I met a monsignor who had forty,” he continued. “But if you have many shoes, give away half.”

“Let us embark on the path of generosity and begin by doing an inspection at home. What do I not need, what could be useful for someone else, a little bit of austerity? Let’s think how to help,” he said.

This, he said, is “a way of being generous, of giving what we have, of sharing.”

This material generosity, thinking of the poor and caring for their needs, so they have something to eat and wear, has another consequence, he said. “It enlarges the heart and leads you to magnanimity.”

“Let us pray to the Lord to free us from that dangerous evil that is consumerism, which seizes you and makes you a slave, with an addiction to spending,” he said.

It is “a psychiatric illness,” he said.

Follow Thomas D. Williams on Twitter .