(from essay by Cardinal Müller, see citation at bottom of page)
The doctrine of the indissolubility of marriage is often met with incomprehension in a secularized environment. Where the fundamental insights of Christian faith have been lost, church affiliation of a purely conventional kind can no longer sustain major life decisions or provide a firm foothold in the midst of marital crises–as well as crises in priestly and religious life. Many people ask, how can I bind myself to one woman or one man for an entire lifetime? Who can tell me what my marriage will be like in ten, twenty, thirty, or forty years? Is a definite bond to one person possible at all? The many marital relationships that founder today reinforce the skepticism of young people regarding definitive life choices.
On the other hand, the ideal–built into the order of creation–of faithfulness between one man and one woman has lost none of its fascination, as is apparent from recent opinion surveys among young people. Most of them long for a stable, lasting relationship, in keeping with the spiritual and moral nature of the individual person. Moreover, one must not forget the anthropological value of indissoluble marriage: it withdraws the spouses from caprice and from the tyranny of feelings and moods. It helps them to survive personal difficulties and to overcome painful experiences. Above all, it protects the children, who have the most to suffer from marital breakdown.
Love is more than a feeling or an instinct. Of its nature it is self-giving. In marital love two people say consciously and intentionally to one another, only you–and you for ever. The word of the Lord, “what therefore God has joined together” (Mk 10:9; Mt 19:6), corresponds to the promise of the spouses: “I take you as my husband….I take you as my wife….I will love, esteem, and honor you, as long as I live, till death us do part.” The priest blesses the covenant that the spouses have sealed with one another before God. If anyone should doubt whether the marriage bond is ontological, let him learn from the word of God: “Have you not read that he who made them from the beginning made them male and female, and said, ‘For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one’? So they are no longer two but one” (Mk 10:5-0; Mt 19:4-6).
For Christians, the marriage of baptized persons incorporated into the Body of Christ has a sacramental character and therefore represents a supernatural reality. A serious pastoral problem arises from the fact that many people today judge Christian marriage exclusively by worldly and pragmatic criteria. Those who think according to the “spirit of the world” (1 Cor 2:12) cannot understand the sacramentality of marriage. The Church cannot respond to the growing incomprehension of the sanctity of marriage by pragmatically accomodating the supposedly inevitable, but only by trusting in “the Spirit which is from God, that we might understnad the gifts bestowed on us by God” (1 Cor 2:12). Sacramental marriage is a testimony to the power of grace, which changes man and prepares the whole Church for the holy city, the new Jerusalem, the Church, which is prepared “as a bride adorned for her husband” (Rev 21:2). The gospen of the sanctity of marriage is to be proclaimed with prophetic candor. By adapting to the spirit of the age, a weary prophet seeks his own salvation but not the salvation of the world in Jesus Christ. Faithfulness to marital consent is a prophetic sign of the salvation that God bestows upon the world. “He who is able to receive this, let him receive it” (Mt 19:12). Through sacramental grace, married love is purified, strengthened, and ennobled. “Sealed by mutual faithfulness and hallowed above all by Christ’s sacrament, this love remains steadfastly true in body and in mind, in bright days or dark. It will never be profaned by adultery or divorce” (Gaudium et Spes 49). In the strength of the sacrament of marriage, the spouses participate in God’s definitive, irrrevocable love. They can therefore be witnesses of God’s faithful love, but they must nourish their love constantly through living by faith and love.
(Gerhard Ludwig Cardinal Müller, Prefect of the Congregation for the Doctrine of the Faith, p 159-161 in Remaining in the Truth of Christ, Marriage and Communion in the Catholic Church; edited by Robert Dodaro, Ignatius Press 2014)