13 In addition to its important link with the entirety of the Church's social doctrine, Populorum Progressio is closely connected to the overall magisterium of Paul VI , especially his social magisterium. His was certainly a social teaching of great importance: he underlined the indispensable importance of the Gospel for building a society according to freedom and justice, in the ideal and historical perspective of a civilization animated by love. Paul VI clearly understood that the social question had become worldwide and he grasped the interconnection between the impetus towards the unification of humanity and the Christian ideal of a single family of peoples in solidarity and fraternity. In the notion of development, understood in human and Christian terms, he identified the heart of the Christian social message , and he proposed Christian charity as the principal force at the service of development. Motivated by the wish to make Christ's love fully visible to contemporary men and women, Paul VI addressed important ethical questions robustly, without yielding to the cultural weaknesses of his time.
Source: Caritas in Veritate (Vatican.va)