Modern Catholic social teaching is the body of social principles and moral teaching that is articulated in the papal, conciliar, and other official documents issued since the late nineteenth century and dealing with the economic, political, and social order. This teaching is rooted in the Hebrew and Christian Scriptures as well as in traditional philosophical and theological teachings of the Church.
All must consider it their sacred duty to count social obligations among their chief duties today and observe them as such. For the more closely the world comes together, the more widely do people's obligations transcend particular groups and extend to the whole world. This will be realized only if individuals and groups practise moral and social virtues and foster them in social living. Then, under the necessary help of divine grace, there will arise a generation of new women and men, the molders of a new humanity. The Church in the Modern World (#30)
One of the gravest errors of our time is the dichotomy between the faith which many profess and their day-to-day conduct. As far back as the Old Testament the prophets vehemently denounced this scandal, and in the New Testament Christ himself even more forcibly threatened it with severe punishment.
Let there, then, be no such pernicious opposition between professional and social activity on the one hand and religious life on the other. Christians who shirk their temporal duties shirk their duties towards his neighbor, neglect God himself, and endanger their eternal salvation. The Church in the Modern World (#43)
Christ did not bequeath to the church a mission in the political, economic, or social order: the purpose he assigned to it was religious. But this religious mission can be the source of commitment, direction, and vigor to establish and consolidate the human community according to the law of God.
In fact, the church is able, indeed it is obliged, if times and circumstances require it, to initiate action for the benefit of everyone, especially of those in need, such as works of mercy and the like. The Church in the Modern World (#42)
Church, State, and Society by 
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