Consequently the decisive answer to every one of man’s questions, his religious and moral questions in particular, is given by Jesus Christ, or rather is Jesus Christ himself […] Jesus Christ, the ‘light of the nations’, shines upon the face of his Church, which he sends forth to the whole world to proclaim the Gospel to every creature (Mk 16:15). Hence the Church, as the People of God among the nations, (cf. Lumen Gentium, 9) while attentive to the new challenges of history and to mankind’s efforts to discover the meaning of life, offers to everyone the answer which comes from the truth about Jesus Christ and his Gospel. (John Paul II. Encyclical Veritatis splendor, no. 2, August 6, 1993)

In the field of conjugal morality the Church is Teacher and Mother and acts as such. As Teacher, she never tires of proclaiming the moral norm that must guide the responsible transmission of life. The Church is in no way the author or the arbiter of this norm. In obedience to the truth which is Christ, whose image is reflected in the nature and dignity of the human person, the Church interprets the moral norm and proposes it to all people of good will, without concealing its demands of radicalness and perfection. (John Paul II. Apostolic Exhortation Familiaris consortio, no. 33, November 22, 1981)

Human frailty grows if the divorce mentality dominates, something that the Council denounced with such vigour because it leads so often to separations and definitive break-ups. Even a bad education for sexuality harms the life of the family. When there is lacking an integral preparation for marriage that respects the gradual stages of the maturation of the engaged couple (cf. Familiaris consortio, n. 66), in the family this lessens the possibility of defence. There is no difficult situation that cannot be adequately confronted when one cultivates a genuine atmosphere of Christian life. Love itself, wounded by sin, is still a redeemed love (cf. CCC, n. 1608). It is clear that, if sacramental life is weak, the family yields more easily to snares because it is deprived of any defences. (John Paul II. Address to the participants in the Plenary Assembly of the Pontifical Council for the Family, no. 3, October 18, 2002)

The Church knows the path by which the family can reach the heart of the deepest truth about itself. The Church has learned this path at the school of Christ and the school of history interpreted in the light of the Spirit. She does not impose it but she feels an urgent need to propose it to everyone without fear and indeed with great confidence and hope, although she knows that the Good News includes the subject of the Cross. But it is through the Cross that the family can attain the fullness of its being and the perfection of its love. (John Paul II. Apostolic Exhortation Familiaris consortio, no. 86, November 22, 1981)

Faced with the difficulties and the resources of the family today, the Church feels called to renew the awareness of the responsibility that it received from Christ with respect to the precious gift of matrimony and the family: the task of announcing it in its truth, of celebrating it in its mystery and of living it within daily existence by those who ‘God calls to serve him in matrimony.’ (John Paul II. Address to the representatives of the Episcopal Conferences on the 20th year of the Encyclical Humanae vitae, November 7, 1988)

I am aware of your commitment to defending and promoting this institution which has its origin in God and in his plan of salvation (cf. Familiaris consortio, n. 49). Today we are seeing a trend, very widespread in certain areas, which is tending to reduce its true nature. Indeed, there is no lack of attempts, in public opinion and in civil legislation, to make equivalent to the family mere de facto unions or to recognize as such same-sex unions. These and other anomalies lead us with pastoral firmness to proclaim the truth about marriage and the family. Not to do so would be a serious pastoral omission that would lead people into error, especially those who have the important responsibility of making decisions for the common good of the nation. (John Paul II. Address to the Bishops of Brazil (Leste II) on their ad limina visit, November 16, 2002)

Today it is more urgent than ever […] to rediscover the value of the family, as a community based on the indissoluble matrimony of one man and one woman who in love establish their existence together and open themselves to the gift of life […]. The rediscovery of this original divine plan is of decisive importance, within the crises that humanity is passing through in our times. (John Paul II. Angelus, no. 2, December 26, 1993)

Illuminated by the faith that gives her an understanding of all the truth concerning the great value of marriage and the family and their deepest meaning, the Church […] The Church is deeply convinced that only by the acceptance of the Gospel are the hopes that man legitimately places in marriage and in the family capable of being fulfilled. Willed by God in the very act of creation (cf. Gen 1-2), marriage and the family are interiorly ordained to fulfillment in Christ (cf. Eph 5) and have need of His graces in order to be healed from the wounds of sin (cf. GS 47; John Paul II, Apopropinquat Iam) and restored to their ‘beginning’(cf. Mt 19:4), that is, to full understanding and the full realization of God’s plan. At a moment of history in which the family is the object of numerous forces that seek to destroy it or in some way to deform it, and aware that the well-being of society and her own good are intimately tied to the good of the family, the Church perceives in a more urgent and compelling way her mission of proclaiming to all people the plan of God for marriage and the family. (John Paul II. Apostolic Exhortation Familiaris consortio, no. 86, November 22, 1981)

The family constitutes the fundamental ‘cell’ of society. But Christ—the ‘vine’ from which the ‘branches’ draw nourishment—is needed so that this cell will not be exposed to the threat of a kind of cultural uprooting which can come both from within and from without. Indeed, although there is on the one hand the ‘civilization of love’, there continues to exist on the other hand the possibility of a destructive ‘anti-civilization’, as so many present trends and situations confirm. (John Paul II. Letter to Families Gratissimam sane, February 2, 1994)

Hence there is urgent need of a broad catechetical effort regarding the Christian ideal of conjugal communion and family life […] Also required is a serious preparation of young people for marriage, one which clearly presents Catholic teaching on this sacrament at the theological, anthropological and spiritual levels. […] Families should not fail to set time aside for prayer, in which spouses are united with each other and with their children. There is a need to encourage shared spiritual moments such as participating in the Eucharist on Sundays and Holy Days, receiving the Sacrament of Reconciliation, daily prayer in the family and practical signs of charity. This will strengthen fidelity in marriage and unity in families. (John Paul II. Apostolic Exhortation Ecclesia in America, no. 46, January 22, 1999)

In today’s world, where certain erroneous concepts concerning the human being, freedom and love are spreading, we must never tire of presenting anew the truth about the family institution, as God has desired it since creation. […] In our day it is especially the stability of the family that is at risk; to safeguard it one often has to swim against the tide of the prevalent culture, and this demands patience, effort, sacrifice and the ceaseless quest for mutual understanding. Today, however, it is possible for husbands and wives to overcome their difficulties and remain faithful to their vocation with recourse to God’s support, with prayer and participating devotedly in the sacraments, especially the Eucharist. (Benedict XVI. Address to the participants in the plenary assembly of the Pontifical Council for the Family, May 13, 2006)

This pastoral commitment is made more urgent by the growing crisis of married life and the declining birth rate. […] It is within the complexity of these situations that you are called to promote the Christian meaning of life through the explicit proclamation of the Gospel, brought with gentle pride and great joy to the various milieus of daily life. From faith lived with courage, today as in the past, flows a rich culture of love for life, from conception until its natural end, the promotion of human dignity, of the elevation of the importance of the family based on faithful marriage and open to life, and of the commitment to justice and solidarity. The cultural changes taking place are asking you to be committed Christians. (Benedict XVI. Pastoral Visit to Aquileia and Venice: address to the Preparatory Assembly for the Second Ecclesial convention of Aquileia, May 7, 2011)

Your duty as Pastors consists in presenting in its full richness the extraordinary value of marriage, which as a natural institution is a ‘patrimony of humanity’. Moreover, its elevation to the loftiest dignity of a sacrament must be seen with gratitude and wonder. […] Today, it is necessary to proclaim with renewed enthusiasm that the Gospel of the family is a process of human and spiritual fulfilment in the certainty that the Lord is always present with his grace. This proclamation is often distorted by false concepts of marriage and the family that do not respect God’s original plan. In this regard, people have actually reached the point of suggesting new forms of marriage, some unknown to popular cultures in that its specific nature is altered. (Benedict XIV. Address to the participants of the Meeting of Presidents of Latin American Episcopal Commissions for the Family and Life, December 3, 2005)

It is to be anticipated that perhaps not everyone will easily accept this particular teaching. There is too much clamorous outcry against the voice of the Church, and this is intensified by modern means of communication. But it comes as no surprise to the Church that she, no less than her divine Founder, is destined to be a ‘sign of contradiction’ (Lk 2:34). She does not, because of this, evade the duty imposed on her of proclaiming humbly but firmly the entire moral law, both natural and evangelical. […] In preserving intact the whole moral law of marriage, the Church is convinced that she is contributing to the creation of a truly human civilization. […] The Church, in fact, cannot act differently toward men than did the Redeemer. She knows their weaknesses, she has compassion on the multitude, she welcomes sinners. But at the same time she cannot do otherwise than teach the law. For it is in fact the law of human life restored to its native truth and guided by the Spirit of God (cf. Rom 8). (Paul VI. Encyclical Humanae vitae, nos. 18, 19, July 25, 1969)

Consequently, since everything must be referred to the law and mind of God, in order to bring about the universal and permanent restoration of marriage, it is indeed of the utmost importance that the faithful should be well instructed concerning matrimony; both by word of mouth and by the written word, not cursorily but often and fully, by means of plain and weighty arguments, so that these truths will strike the intellect and will be deeply engraved on their hearts. Let them realize and diligently reflect upon the great wisdom, kindness and bounty God has shown towards the human race, not only by the institution of marriage, but also, and quite as much, by upholding it with sacred laws; still more, in wonderfully raising it to the dignity of a Sacrament by which such an abundant fountain of graces has been opened to those joined in Christian wedlock, that these may be able to serve the noble purposes of wedlock for their own welfare and for that of their children, of the community and also for that of human relationship. (Pius XI. Encyclical Casti connubii, no. 105, December 31, 1930)

This family Christian training sadly undermined in these our times, cannot possibly be restored to its due dignity, save by those laws under which it was established in the Church by her Divine Founder Himself. Our Lord Jesus Christ, by raising to the dignity of a sacrament the contract of matrimony, in which He would have His own union with the Church typified, not only made the marriage tie more holy, but, in addition, provided efficacious sources of aid for parents and children alike, so that, by the discharge of their duties one to another, they might with greater ease attain to happiness both in time and in eternity. (Leo XIII. Encyclical Inscrutabili Dei consilio, no. 10, April 21, 1878)

By coming to restore the original order of creation disturbed by sin, he himself gives the strength and grace to live marriage in the new dimension of the Reign of God. It is by following Christ, renouncing themselves, and taking up their crosses that spouses will be able to ‘receive’ the original meaning of marriage and live it with the help of Christ (Mt 19:11). This grace of Christian marriage is a fruit of Christ’s cross, the source of all Christian life. (Catechism of the Catholic Church, no. 1615)

It is up to the Bishops to instruct the faithful in the moral teaching concerning sexual morality, however great may be the difficulties in carrying out this work in the face of ideas and practices generally prevailing today. This traditional doctrine must be studied more deeply. It must be handed on in a way capable of properly enlightening the consciences of those confronted with new situations. (Congregation for the Doctrine of the Faith, Persona humana,  Declaration on certain questions regarding sexual ethics,  no. 13, December 29, 1975)