1. The Church’s mission in the world
The salvation achieved by Christ, and hence the mission of the Church, is directed to the human person in his or her integral being. Hence when the Church sets forth her social doctrine, not only is she not departing from her mission, but rather she is faithfully fulfilling it. Moreover, evangelization would not be authentic if it did not take into account the relationship between the Gospel and personal behavior, both at the individual and social level. The Church carries out her activity in the world and should be related to it harmoniously, by respecting the structure and finality of the various human organizations.
Thus the Church has the mission, and also the right, to be concerned about social problems. In doing so “she can not be accused of going outside her own specific field of competence and, still less, outside the mandate received from the Lord.” 
The Church’s mission in this area is not limited to setting forth ethical guidelines. Rather it entails making clear the implications of the Gospel for social life, in accord with the integral truth about man, and the conduct this entails, while urging people to make it a reality in the world.
A deep and essential union exists between Christian life and human development.  But this harmony does not imply confusing the two domains. The goal of Christian conduct is identification with Christ. The liberation Jesus brings is at its core liberation from sin, which certainly also requires striving to further human liberation in the earthly domain.  This distinction is the basis for the autonomy of earthly realities
The teachings of the Magisterium in this area do not, therefore, touch on technical aspects or propose systems of social organization. Rather they seek to foster the formation of people’s consciences, without compromising the autonomy of temporal realities. 
Hence the hierarchy does not have a direct role in the organization of society; its task is to teach and interpret the moral principles in this area in an authentic way. The Church accepts any social system that respects human dignity, while the faithful should receive her social teaching with an adherence of intellect, will and deeds (cf. Lk 10:16; Catechism of the Catholic Church , 2032 and 2037).
2. Relationship between the Church and the State
Religion and politics, although distinct in their scope, are not separate realms, since each person is called to fulfill his or her religious duties in tandem with the social, economic and political duties that fall to each citizen. Nevertheless, “the faithful should learn to distinguish carefully between the rights and the duties which are theirs as members of the Church, and those which they have as members of human society. They will strive to unite the two harmoniously, remembering that in every temporal affair they are to be guided by a Christian conscience, since not even in temporal business may any human activity be withdrawn from God’s dominion. In our times it is most necessary that this distinction and harmony should shine forth as clearly as possible in the manner in which the faithful act, in order that the mission of the Church may correspond more fully with the special circumstances of the world today.”  These words can be seen as showing Catholics today how to live our Lord’s teaching: Render therefore to Caesar the things that are Caesar’s, and to God the things that are God’s ( Mt . 22:21).
The relationship between the Church and the State entails, therefore, a distinction without separation, a union without confusion. (cf. Mt 22:15-21 and parallels). This relationship will be correct and fruitful if three fundamental principles are kept in mind: accepting a sphere of moral values that precede and guide the political sphere; distinguishing the mission of religion from that of politics; fostering the collaboration between both spheres.
a) Moral values should guide political life
The proposal of a so-called “ethical state” that seeks to regulate the behavior of its citizens, is today broadly rejected, since it frequently leads to totalitarianism or at least implies a markedly authoritarian tendency. It is not the State’s role to decide what is good or what is evil; rather it has the obligation to seek and promote the common good, and to do so it will sometimes need to make laws concerning the behavior of its citizens.
This rejection of an “ethical state” should not, however, lead to the opposite error: upholding the moral “neutrality” of the State, which does not nor can not exist. The State needs to be informed by moral values that foster the integral development of persons, and that development, in its social dimension, forms part of the earthly common good.
b) The Church and the State differ in their nature and aims
The Church has received its apostolic mandate from Christ: Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit ( Mt 28:19-20). With her doctrine and apostolic activity, the Church contributes to the right ordering of temporal realities, so that these may help men and women attain their ultimate end and not lead them astray.
The means the Church employs to carry out her mission are, above all, spiritual: preaching the Gospel, administering the Sacraments, prayer. She also needs to use material means, appropriate to the embodied nature of human persons (cf. Acts 4:32-37; 1 Tim 5:18), means which must always be in conformity with the Gospel. In addition, the Church should dispose of the independence needed to carry out her mission in the world, but not political or economic dominion (cf. Catechism of the Catholic Church , 2246; Compendium of the Social Doctrine of the Church , 426). 
The aim of the State is the earthly common good of civil society; this good is not only material but also spiritual, since the members of society are persons with a body and a soul. Social progress requires, besides material goods, many other goods of a spiritual nature: peace, order, justice, freedom, security, etc. These goods can only be achieved through the exercise of social virtues, which the State should foster and safeguard (for example, public morality).
The difference between the religious and political sphere entails that the State does not enjoy a “sacred” character nor should it govern people’s consciences, since the moral foundation of politics lies outside its provenance. In addition, the Church does not possess coercive political power; her power is a spiritual one, and should never seek to impose any single political solution. Thereby the State and Church adhere to their own proper functions, fostering religious and social freedom.
From here stem two important rights: the Church’s right to religious freedom, which consists in immunity from coercion on the part of the State in religious matters; and the right of Catholics to freedom of action with respect to the hierarchy in temporal matters, although with the obligation of following the Magisterium (cf. C.I.C ., canon 227). Moreover, “by preaching the truths of the Gospel, and bringing to bear on all fields of human endeavor the light of her doctrine and of a Christian witness, the Church respects and fosters the political freedom and responsibility of citizens.” 
c) Collaboration between Church and State
The distinction between the Church and the State does not imply (as mentioned above) a total separation, nor does it mean that the Church should restrict her activity to the private and spiritual sphere. Certainly the Church “cannot and must not replace the State. Yet at the same time she cannot and must not remain on the sidelines in the fight for justice.”  Therefore the Church has the right and the duty “to teach her social doctrine, to exercise her role freely among men, and also to pass moral judgment in those matters which regard public order when the fundamental rights of the human person or the salvation of souls require it.” 
Thus, for example, the Church can and should declare that a law is unjust because it is contrary to the natural law (laws on abortion or divorce), or that certain customs or situations are immoral even though permitted by the civil power, or that Catholics should not lend their support to persons or parties that set forth goals contrary to the law of God, and therefore to the dignity of the human person and to the common good. 
Both the Church and those who govern society are seeking to serve mankind (although under different titles), and they “will carry out this service with greater efficacy, for the good of all, the healthier and better is the cooperation between them.” 
The practical ways of regulating these relations can vary according to circumstances: for example, they will not be the same in countries with a Catholic tradition as in others in which the presence of Catholics is a minority.
An essential right that should always be safeguarded is the protection of religious freedom.  Ensuring respect for this right means ensuring respect for the entire social order. The right to social and civil freedom in religious matters is the source and synthesis of all human rights. 
In many countries the constitution or civil laws guarantee religious freedom for all citizens and religious groups; thus the Church can find sufficient freedom to fulfill her mission and space to carry out her apostolic initiatives. 
Also where possible, the Church can establish agreements with the State, generally referred to as Concordats, in which specific solutions are agreed upon related to the interaction of the State and the Church: the freedom to carry out her mission, agreements on economic matters, feast days, etc.
3. Jurisdiction in “mixed matters”
There are matters in which both the Church and the State should intervene according to their respective competencies and goals (called “mixed matters”); these include education, marriage, social media, and assistance for the needy.  In these matters, collaboration is particularly necessary, so that each one can achieve its own mission without any impediment by the other. 
a) The Church has the right to regulate the marriage of Catholics, even when only one of the spouses is Catholic; among other reasons, because marriage is a sacrament and the Church is responsible for establishing norms for how it is administered. While the State has the responsibility to regulate its civil effects: the division of goods between the spouses, etc. (cf. C.I.C. , canon 1059). The State has the duty to recognize the right of Catholics to contract canonical marriage.
b) The education of children, also in religious matters, is the responsibility of the parents by natural law; they are the ones who ought to determine the teaching they wish their children to receive, the school or catechism class they will attend, etc.  Where there is insufficient initiative on the part of parents or social groups, the State should subsidiarily establish its own schools, always respecting the parents’ right to choose the orientation of their children’s education.
The parents also have the right to establish and direct schools in which their children can receive an appropriate education, which given their social value should be recognized and subsidized by the State.  And they have the right that their children receive at school—also when state run—teaching in accord with their religious convictions. 
The State has the right to establish norms related to educational matters required by the common good (access to instruction for everyone, minimum requirements, recognition of diplomas, etc.). For the State to reserve education to itself as a monopoly, even if indirectly, is tyranny (cf. C.I.C. , 797).
It always falls to the Church to determine and watch over all that refers to the teaching and spread of the Catholic religion: programs, content, books, teacher qualifications. This is part of the Church’s right to defend and guarantee her own identity and the integrity of her doctrine. No one, therefore, can presume to teach Catholic doctrine (in schools at any level) if he or she is not approved by the ecclesiastical authority (cf. C.I.C ., 804-805).
c) The Church also has the right to promote social undertakings consistent with her religious mission (hospitals, communications media, orphanages, shelters), as well as the right that the State recognize these “Catholic” undertakings with the same conditions as initiatives promoted by other parties (tax exemptions, qualification of employees, subsidies, possibility of collecting donations, etc.).
4. Secularity and secularism
A very relevant topic today is the distinction between secularity and secularism. Secularity means that the State is autonomous with respect to ecclesiastical laws, while secularism claims the autonomy of the political realm from the moral order and divine plan, and tends to restrict religion to the sphere of the purely private. In this way it violates the right to religious freedom and harms the social order (cf. Compendium of the Social Doctrine of the Church , 572). An authentic secularity avoids two extremes: the attempt to transform civil society into the arbiter of morals,  and the a priori rejection of the moral values stemming from culture, religion, etc., which people adhere to freely and which should not be dictated from the seat of power. 
It should also be emphasized that it is illusory and unjust to ask the faithful to act in the political realm “as if God did not exist.” Every person acts on the basis of his or her cultural convictions (be they religious, philosophical, political, etc.), whether derived from religious faith or not; these are convictions, therefore, that influence the social behavior of citizens. .
Acting in the political realm in accord with one’s own faith, if consistent with the dignity of the human person, does not mean subordinating politics to religion. It means that politics is at the service of persons and therefore ought to respect moral demands, which is simply to say that it should respect and foster the dignity of every human being.
5. Pluralism in the social sphere among Catholics
All the above accords with the legitimate pluralism of Catholics in the social sphere. The same good objectives can be achieved by different pathways; it is reasonable, therefore, that there be a pluralism of opinions on how to achieve a specific social goal. It is natural that the backers of each solution legitimately seek to carry it out. Nevertheless, no option has the guarantee of being the only appropriate alternative (among other reasons because politics to a great extent is concerned with future events, and thus is the art of the possible), and even less so, of being the only one that accords with the Church’s teaching.  “No one is allowed in the aforementioned situations to appropriate the Church’s authority for his opinion.” 
Therefore all the faithful, particularly the laity, have the right that their legitimate autonomy be recognized in the Church to take part in temporal affairs in accord with their own convictions and preferences, as long as these are in agreement with Catholic teaching. And they have the duty not to implicate the Church in their own decisions and social activity, never presenting their solutions as “Catholic” solutions. 
Pluralism, while a positive good, should never be confused with ethical relativism.  Pluralism is morally admissible when the goal is a true personal or social good; but not if the decision is contrary to the natural law, to public order, and to the fundamental rights of the human person (cf. Catechism of the Social Doctrine of the Church , 1901). But outside these extreme cases, pluralism should be fostered in temporal matters, as a good for personal, social, and ecclesial life.
Catechism of the Catholic Church , 2104-2109; 2244-2246; 2419-2425.
Vatican II, Const. Gaudium et spes , 74-76; Decl. Dignitatis humanae , 1-8; 13-14.
John Paul II, Apost. Exhort. Christifideles laici , December 39, 1988, 36-44.
Saint Josemaria, Homily “Passionately Loving the World,” in Conversations with Msgr. Escrivá de Balaguer , 113-123.
Congregation for the Doctrine of the Faith, Doctrinal Note on Some Questions Regarding the Participation of Catholics in Political Life , November 24, 2002.
Compendium of the Social Doctrine of the Church , 49-55; 60-71; 189-191; 238-243; 377-427.
 John Paul II, Enc . Sollicitudo rei socialis , December 30, 1987, 8. Cf. Paul VI, Apost..Exhort. Evangelii nuntiandi , December 8, 1975, 29 and 30; John Paul II, Discourse in Puebla, III; Enc. Redemptor hominis , March 4, 1979, 15; Compendium of the Social Doctrine of the Church , 64 and 71.
 Cf. Paul VI, Apost. Exhort. Evangelii nuntiandi , 31. Uniting the human with the divine is very proper to Opus Dei. The Founder said that the entire life of its faithful is “a service with exclusively supernatural aims, because Opus Dei is not, and will never be—nor could it be—a tool for temporal ends. But at the same time, it is a service to mankind, because all you are doing is trying in an upright way to achieve Christian perfection, acting most feely and responsibly in all the areas of civil life. It is a self-sacrificing service that is not degrading, but uplifting; it expands the heart (making it more Roman , in the most noble meaning of the word) and leads one to pursue the honor and the good of people of every nation—to try to see that every day there are fewer people who are poor and uneducated, fewer souls without faith, without hope; fewer wars, less uncertainty, more charity and peace” (St. Josemaría, Letter , May 31, 1943, no. 1; in J. L. Illanes, F. Ocáriz, P. Rodríguez, Opus Dei in the Church , Scepter Publishers, p. 131.
 Cf. Paul VI, Apost. Exhort. Evangelii nuntiandi , 9, 33-35; Congregation for the Doctrine of the Faith, Instr. Libertatis conscientia , March 23, 1986, 23.
 Speaking of the values that foster the development of human dignity, the Compendium states: “Respect for the legitimate autonomy of earthly realities prompts the Church not to claim specific competence in the technical or temporal order; but it does not prevent her from intervening to show to how, in the different choices made by men and women, these values are either affirmed or denied” ( Compendium of the Social Doctrine of the Church , 197). Cf. Vatican Council II, Gaudium et spes , 36 and 42; Paul VI, Enc. Populorum progressio , March 26, 1967, 13; Juan Pablo II, Enc. Sollicitudo rei socialis , 41; Compendiim , 68 and 81.
 Vatican Council II, Const. Lumen gentium, 36. Cf. Cathechism of the Catholic Church, 912.
 Cf. Vatican Council II, Const. Gaudium et spes , 76; Decl. Dignitatis humanae , 13.
 Vatican Council II, Const. Gaudium et spes , 76.
 Benedict XVI, Enc. Deus caritas est , December 25, 2005, 28. Cf. Benedict XVI, Discourse in Verona , October 19, 2006.
 Vatican Council II, Const. Gaudium et spes , 76.
 Cf. Ibid., 40 and 41.
 Ibid ., 76. Cf. Compendium of the Social Doctrine of the Church , 425.
 This right does not consist in the freedom before God to choose any religion one pleases, because there is only one true religion and all men and women have the obligation to seek the truth and, once found, to embrace it (cf. Vatican Council II, Decl. Dignitatis humanae , 1). The right to religious freedom means that “all men are to be immune from coercion on the part of individuals or of social groups and of any human power, in such wise that no one is to be forced to act in a manner contrary to his own beliefs, whether privately or publicly, whether alone or in association with others, within due limits” (Vatican Council II, Decl. Dignitatis humanae , 2).
“Respect on the part of the State for the right to religious freedom is a sign of respect for the other basic human rights, because it is the implicit recognition of an order that transcends the political dimension of life” (John Paul II, Discourse, January 9, 1989, 6).
 Cf. John Paul II, Enc. Centesimus annus , May 1,1991, 47. The right to freedom in the sphere of religion “is tied to all the other freedoms;” moreover, all of these “require it as a foundation” (John Paul II, Discourse, March 23, 1991, 2).
 Cf. Vatican Council II, Decl. Dignitatis humanae , 13.
 Whenever circumstances allow it, the Holy See seeks to establish diplomatic relations with the world’s countries in order to keep open a channel of permanent dialogue in the questions that concern both parties.
 “It is not true that there is opposition between being a good Catholic and serving civil society faithfully. In the same way there is no reason why the Church and the State should clash when they proceed with the lawful exercise of their respective authorities, in fulfilment of the mission God has entrusted to them” (St. Josemaría, Furrow , 301).
 “The right and the duty of parents to educate their children are primordial and inalienable.” ( Catechism of the Catholic Church , 2221). Cf.. John Paul II, Apost. Exhort. Familiaris consortio , November 22,1981, 36.
 Cf. John Paul II, Apost. Exhort. Familiaris consortio , 40.
 “As those first responsible for the education of their children, parents have the right to choose a school for them which corresponds to their own convictions. This right is fundamental. As far as possible parents have the duty of choosing schools that will best help them in their task as Christian educators. Public authorities have the duty of guaranteeing this parental right and of ensuring the concrete conditions for its exercise” ( Catechism of the Catholic Church , 2229).
 Cf. Paul VI, Apost. Letter Octogesima adveniens , May 14, 1971, 25; John Paul II, Enc. Centesimus annus , 25.
 Cf. Congregation for the Doctrine of the Faith, Doctrinal Note on Some Questions Regarding the Participation of Catholics in Political Life , November 24, 2002, 6; Compendium of the Social Doctrine of the Church , 571.
 Cf. Vatican Council II, Const. Gaudium et spes , 75; Paul VI, Apost. Letter, Octogesima adveniens , 50; Compendium of the Social Doctrine of the Church , 417.
 Ibid ., 43.
 Cf. St. Josemaría, Conversations , 117
 “Such relativism, of course, has nothing to do with the legitimate freedom of Catholic citizens to choose among the various political opinions that are compatible with faith and the natural moral law, and to select, according to their own criteria, what best corresponds to the needs of the common good. Political freedom is not—and cannot be—based upon the relativistic idea that all conceptions of the human person’s good have the same value and truth, but rather, on the fact that politics are concerned with very concrete realizations of the true human and social good in given historical, geographic, economic, technological and cultural contexts. From the specificity of the task at hand and the variety of circumstances, a plurality of morally acceptable policies and solutions arises” ( Doctrinal Note on Some Questions Regarding the Participation of Catholics in Political Life , November 24, 2002, 3). Cf. Compendium of the Social Doctrine of the Church , 569 and 572.