23 "He who has the goods of this world and sees his brother in need and closes his heart to him, how does the love of God abide in him?" (21) Everyone knows that the Fathers of the Church laid down the duty of the rich toward the poor in no uncertain terms. As St. Ambrose put it: "You are not making a gift of what is yours to the poor man, but you are giving him back what is his. You have been appropriating things that are meant to be for the common use of everyone. The earth belongs to everyone, not to the rich." (22) These words indicate that the right to private property is not absolute and unconditional. No one may appropriate surplus goods solely for his own private use when others lack the bare necessities of life. In short, "as the Fathers of the Church and other eminent theologians tell us, the right of private property may never be exercised to the detriment of the common good." When "private gain and basic community needs conflict with one another," it is for the public authorities "to seek a solution to these questions, with the active involvement of individual citizens and social groups." (23)
Source: Populorum Progressio (Vatican.va)