8 In 1967, when he issued the Encyclical Populorum Progressio , my venerable predecessor Pope Paul VI illuminated the great theme of the development of peoples with the splendour of truth and the gentle light of Christ's charity. He taught that life in Christ is the first and principal factor of development and he entrusted us with the task of travelling the path of development with all our heart and all our intelligence , that is to say with the ardour of charity and the wisdom of truth. It is the primordial truth of God's love, grace bestowed upon us, that opens our lives to gift and makes it possible to hope for a “development of the whole man and of all men” , to hope for progress “from less human conditions to those which are more human” , obtained by overcoming the difficulties that are inevitably encountered along the way. At a distance of over forty years from the Encyclical's publication, I intend to pay tribute and to honour the memory of the great Pope Paul VI, revisiting his teachings on integral human development and taking my place within the path that they marked out, so as to apply them to the present moment. This continual application to contemporary circumstances began with the Encyclical Sollicitudo Rei Socialis , with which the Servant of God Pope John Paul II chose to mark the twentieth anniversary of the publication of Populorum Progressio . Until that time, only Rerum Novarum had been commemorated in this way. Now that a further twenty years have passed, I express my conviction that Populorum Progressio deserves to be considered “the Rerum Novarum of the present age”, shedding light upon humanity's journey towards unity.
Source: Caritas in Veritate (Vatican.va)