81 We appeal, first of all, to Our sons. In the developing nations and in other countries lay people must consider it their task to improve the temporal order. While the hierarchy has the role of teaching and authoritatively interpreting the moral laws and precepts that apply in this matter, the laity have the duty of using their own initiative and taking action in this area—without waiting passively for directives and precepts from others. They must try to infuse a Christian spirit into people's mental outlook and daily behavior, into the laws and structures of the civil community. (68) Changes must be made; present conditions must be improved. And the transformations must be permeated with the spirit of the Gospel. We especially urge Catholic men living in developed nations to offer their skills and earnest assistance to public and private organizations, both civil and religious, working to solve the problems of developing nations. They will surely want to be in the first ranks of those who spare no effort to have just and fair laws, based on moral precepts, established among all nations.
Source: Populorum Progressio (Vatican.va)