60 In proclaiming the principles for a solution of the worker question, Pope Leo XIII wrote: "This most serious question demands the attention and the efforts of others". He was convinced that the grave problems caused by industrial society could be solved only by cooperation between all forces. This affirmation has become a permanent element of the Church's social teaching, and also explains why Pope John XXIII addressed his Encyclical on peace to "all people of good will". Pope Leo, however, acknowledged with sorrow that the ideologies of his time, especially Liberalism and Marxism, rejected such cooperation. Since then, many things have changed, especially in recent years. The world today is ever more aware that solving serious national and international problems is not just a matter of economic production or of juridical or social organization, but also calls for specific ethical and religious values, as well as changes of mentality, behaviour and structures. The Church feels a particular responsibility to offer this contribution and, as I have written in the Encyclical Sollicitudo rei socialis, there is a reasonable hope that the many people who profess no religion will also contribute to providing the social question with the necessary ethical foundation. In that same Encyclical I also addressed an appeal to the Christian Churches and to all the great world religions, inviting them to offer the unanimous witness of our common convictions regarding the dignity of man, created by God. In fact I am convinced that the various religions, now and in the future, will have a preeminent role in preserving peace and in building a society worthy of man. Indeed, openness to dialogue and to cooperation is required of all people of good will, and in particular of individuals and groups with specific responsibilities in the areas of politics, economics and social life, at both the national and international levels.
Source: Centesimus Annus (Vatican.va)