Given what we've said about what the Church is, and what relation she ought to have with the Polis (state, country, political unit), how do we start drawing conclusions about what the Church ought to be doing to serve all people?
The second part of the constitution Gaudium et Spes, on the Church in the modern world, lists some key areas where the ministry of the Church is particularly valuable, and ought to be particularly visible. These concerns are marriage and family life (#47ff), development of culture (#53ff), economy and society (#63ff), and politics, both intra-national (#73ff) and inter-national (#77ff). Notice that this list also progresses in the order of subsidiarity, from the smallest and most personal level to the global level. Let's take a quick look at them.
Marriage and Family Life
GS #47: The well-being of the individual person and of human and Christian society is intimately linked with the healthy condition of that community produced by marriage and family. Since the family is the domestic church, and the basic, subsidiary unit of both human and ecclesial life, the Church puts an extremely high priority on protecting and fostering healthy families. Gaudium et Spes lists some threats to married life: polygamy, divorce, fornication, abortion, contraception, worship of self and of pleasure, etc. Therefore the Church's ministry needs to address these kinds of threats, which, of course, we do on a regular basis. Clergy are (as we have always been) on the "front lines" of dealing with issues in marriages, both before and after the fact; and the Church also has resources like Catholic Charities and other Catholic professionals to help protect existing marriages, and heal broken ones (to the extent possible). Catechesis of married adults and their children, and of youth before (both remote and proximate) marriage, takes place constantly. And the witness of married couples themselves is of course critical to the success of these other efforts. All of this also needs to show up regularly in liturgical preaching.
But notice that these efforts to promote marriage and family are also "social justice" efforts. Divorce is the single greatest cause of generational poverty, and the consequences usually fall more heavily on women than men. The outcomes for children of divorced families (education levels, economic status, rates of criminal behavior and both social and physical disease, and stability of their own future marriages) are all significantly lower than for children whose parents do not divorce. All of these things also drive up taxes to support expanding social services, and may tend to imbalance the Church-State relationship and marginalize ecclesial efforts to serve in these areas. The long term costs of abortion and contraception are also devastating, not only morally (as is obvious) but also fiscally (elimination of millions of productive workers, etc, which more and more we are publicly admitting).
So, ecclesial ministry which succeeds in reducing rates of divorce, abortion, contraception, etc, and in strengthening marriage to the same extent, not only serves the individuals who benefit from that ministry directly, but also serves the Church as a whole, and the world in which she lives.
GS #53: Man comes to a true and full humanity only through culture, that is through the cultivation of the goods and values of nature. The "goods and values of nature" are of course many and diverse, and how we "cultivate" them (including both conservation/tradition and innovation/progress) gives us a distinctive "character" at a given time and place. Thus, The word "culture" in its general sense indicates everything whereby man develops and perfects his many bodily and spiritual qualities; he strives by his knowledge and his labor, to bring the world itself under his control. He renders social life more human both in the family and the civic community, through improvement of customs and institutions. Throughout the course of time he expresses, communicates and conserves in his works, great spiritual experiences and desires, that they might be of advantage to the progress of many, even of the whole human family (ibidem).
Gaudium et Spes includes as threats to culture, especially in the modern (urbanizing, industrializing, individualizing) context: technology and the pace of change, commodification of goods and human services, materialism, scientism, deracination, homogenization (loss of traditional wisdom and character), etc.
Obviously, building up families and strengthening marriage also helps preserve and strengthen culture. The human aspects of labor, social relations and engagement, exchange of goods and services, etc., are far less likely to be diminished or lost, when family life is strong and healthy. Family life is the subsidiary reality and model for all social life; its health is the barometer of culture.
In addition, GS #60-61 particularly exhorts the followers of Christ to particular forms of ministry: to support education, while maintaining the Catholic vision of the unity of knowledge within itself (against hyper-specialization in sub-disciplines), and between itself (techne) and morality (sophia); to foster the humanizing aspects of labor; to inculcate a shared commitment to duty (pietas, in its original meaning) to the common good along with personal rights; and to respect the essential differences between men and women, even in the marketplace. Clearly, education is a fundamental ministerial commitment in the Church, not only to our Catholic schools and universities, but also our RE programs, adult bible studies, and sacramental prep, etc. - not to mention upholding the fundamental right of parents to raise their children. In all these ways, the fundamental truth that we must teach is that of the human person: created and loved by God, fallen in Adam, redeemed in Christ, called to and capable of living every aspect of life in intimate union with Christ and thus in the Trinity. Family and ecclesial life, the sacraments and prayer and service must so deeply underlie every individual effort at education/formation that they cannot be separated from it.
In terms of the Church's ministry, clergy have to be present and inherently involved in the life of these institutions. Lay people, with their vocation of bringing all things under Christ's feet by their labor and witness, must work to transform these institutions more deeply into the image of Christ. All the various ways these might take place follow pretty straightforwardly.
Further, while Gaudium et Spes doesn't explicitly go here, there are implied hooks between this document and the other three conciliar Constitutions (Dei Verbum, Lumen Gentium, and especially Sacrosanctum Concilium). This sacred Council has several aims in view: it desires to impart an ever increasing vigor to the Christian life of the faithful; to adapt more suitably to the needs of our own times those institutions which are subject to change; to foster whatever can promote union among all who believe in Christ; to strengthen whatever can help to call the whole of mankind into the household of the Church. The Council therefore sees particularly cogent reasons for undertaking the reform and promotion of the liturgy (SC #1). Culture is never whole without religion, and in religion, liturgy ("cultus")is the primary vehicle of passing on culture. In other words, we cannot pursue social justice or the common good without a solid and enduring foundation in right worship. In short, "Save the liturgy, save the world."
Economy and Society, and Politics
From this it follows that our consistent witness in living for Christ is the engine of divinization in the world. The proclamation of the Gospel in both word and action; the authenticity of standing consistently at the foot of the Cross in all social, economic, and political situations, and in being seen publicly to stand there; and the uncompromising commitment to be the instruments of bringing the order of nature under the order of grace: these are the hallmarks of compelling ecclesial ministry, always and everywhere. For man is the source, the center, and the purpose of all economic and social life (#63). Christians who take an active part in present-day socio-economic development and fight for justice and charity should be convinced that they can make a great contribution to the prosperity of mankind and to the peace of the world. In these activities let them, either as individuals or as members of groups, give a shining example (#70).
Nod to the Natural Law
Note, finally, in this exposition of ecclesiological ministry, the implicit hierarchy of goods. In the commitment of belonging only to Christ, being pro-life comes first, and being pro-family can't really be separated from it. (Of the Ten Commandments, this immediately invokes obedience to #1, 3, 4, 5, and 6.) From these first-order goods comes the second order of "the common good," especially what is tangibly grasped in the concrete life of the community (diocesan Church, local society with vigorously healthy voluntary associations, and deeply shared engagement in economy and political life). This layer of commitment invokes the remaining five Commandments (#2 in right worship in communion with the local bishop, and #7-10 in right social relations with others). Finally, the tertiary order of goods follows, in political commitments and party platforms and identifications. In a truly healthy culture, these various tertiary commitments never differ on the first and second order goods, but may envision different means of achieving them, or may differ on aspects of prudence. How much we argue about the first- and second-order goods is a clear measure of how unhealthy our culture is today, and by implication, how disconnected from that sickness our ministry can be.