From Pope St. John Paul II’s Apostolic Exhortation Familiaris Consortio (1981):
Conjugal communion is characterized not only by its unity but also by its indissolubility: “As a mutual gift of two persons, this intimate union, as well as the good of children, imposes total fidelity on the spouses and argues for an unbreakable oneness between them.”49
It is a fundamental duty of the Church to reaffirm strongly, as the Synod Fathers did, the doctrine of the indissolubility of marriage. To all those who, in our times, consider it too difficult, or indeed impossible, to be bound to one person for the whole of life, and to those caught up in a culture that rejects the indissolubility of marriage and openly mocks the commitment of spouses to fidelity, it is necessary to reconfirm the good news of the definitive nature of that conjugal love that has in Christ its foundation and strength.50
Being rooted in the personal and total self-giving of the couple, and being required by the good of the children, the indissolubility of marriage finds its ultimate truth in the plan that God has manifested in His revelation: He wills and He communicates the indissolubility of marriage as a fruit, a sign and a requirement of the absolutely faithful love that God has for man and that the Lord Jesus has for the Church.
Christ renews the first plan that the Creator inscribed in the hearts of man and woman, and in the celebration of the sacrament of matrimony offers a “new heart”: thus the couples are not only able to overcome “hardness of heart,”51 but also and above all they are able to share the full and definitive love of Christ, the new and eternal Covenant made flesh. Just as the Lord Jesus is the “faithful witness,”52 the “yes” of the promises of God53 and thus the supreme realization of the unconditional faithfulness with which God loves His people, so Christian couples are called to participate truly in the irrevocable indissolubility that binds Christ to the Church His bride, loved by Him to the end.54
The gift of the sacrament is at the same time a vocation and commandment for the Christian spouses, that they may remain faithful to each other forever, beyond every trial and difficulty, in generous obedience to the holy will of the Lord: “What therefore God has joined together, let not man put asunder.”55
To bear witness to the inestimable value of the indissolubility and fidelity of marriage is one of the most precious and most urgent tasks of Christian couples in our time. So, with all my Brothers who participated in the Synod of Bishops, I praise and encourage those numerous couples who, though encountering no small difficulty, preserve and develop the value of indissolubility: thus, in a humble and courageous manner, they perform the role committed to them of being in the world a “sign”—a small and precious sign, sometimes also subjected to temptation, but always renewed—of the unfailing fidelity with which God and Jesus Christ love each and every human being. But it is also proper to recognize the value of the witness of those spouses who, even when abandoned by their partner, with the strength of faith and of Christian hope have not entered a new union: these spouses too give an authentic witness to fidelity, of which the world today has a great need. For this reason they must be encouraged and helped by the pastors and the faithful of the Church.
49 Pastoral Constitution on the Church in the Modern World Gaudium et spes, 48.
50 Cf. Eph 5:25.
51 Cf. Mt 19:8.
52 Rv 3:14.
53 Cf. 2 Cor 1: 20.
54 Cf. Jn 13:1.
55 Mt 19:6.
— Familiaris Consortio 20