11 Since the Creator of all things has established conjugal society as the beginning and basis of human society and, by His grace, has made it a great mystery in Christ and the Church (cf. Eph. 5:32), the apostolate of married persons and families is of unique importance for the Church and civil society. Christian husbands and wives are cooperators in grace and witnesses of faith for each other, their children, and all others in their household. They are the first to communicate the faith to their children and to educate them by word and example for the Christian and apostolic life. They prudently help them in the choice of their vocation and carefully promote any sacred vocation which they may discern in them. It has always been the duty of Christian married partners but today it is the greatest part of their apostolate to manifest and prove by their own way of life the indissolubility and sacredness of the marriage bond, strenuously to affirm the right and duty of parents and guardians to educate children in a Christian manner, and to defend the dignity and lawful autonomy of the family. They and the rest of the faithful, therefore, should cooperate with men of good will to ensure the preservation of these rights in civil legislation and to make sure that governments give due attention to the needs of the family regarding housing, the education of children, working conditions, social security, and taxes; and that in policy decisions affecting migrants their right to live together as a family should be safeguarded. This mission-to be the first and vital cell of society-the family has received from God. It will fulfill this mission if it appears as the domestic sanctuary of the Church by reason of the mutual affection of its members and the prayer that they offer to God in common, if the whole family makes itself a part of the liturgical worship of the Church, and if it provides active hospitality and promotes justice and other good works for the service of all the brethren in need. Among the various activities of the family apostolate may be enumerated the following: the adoption of abandoned infants, hospitality to strangers, assistance in the operation of schools, helpful advice and material assistance for adolescents, help to engaged couples in preparing themselves better for marriage, catechetical work, support of married couples and families involved in material and moral crises, help for the aged not only by providing them with the necessities of life but also by obtaining for them a fair share of the benefits of an expanding economy. At all times and places but particularly in areas where the first seeds of the Gospel are being sown, or where the Church is just beginning, or is involved in some serious difficulty, Christian families can give effective testimony to Christ before the world by remaining faithful to the Gospel and by providing a model of Christian marriage through their whole way of life. To facilitate the attainment of the goals of their apostolate, it can be useful for families to be brought together into groups.
Source: Apostolicam Actuositatem (Vatican.va)