The foundation of sacramental marriage is the unity of the spouses, a bond so intense and grace-filled that it is exclusive and indissoluble, said a document from the Dicastery for the Doctrine of the Faith.
The document, “‘Una Caro’ (One Flesh): In Praise of Monogamy. Doctrinal Note on the Value of Marriage as an Exclusive Union and Mutual Belonging,” was released only in Italian by the Vatican Nov. 25. Pope Leo XIV approved its contents Nov. 21 and authorized its publication.
“Although each marital union is a unique reality, embodied within human limitations, every authentic marriage is a unity composed of two individuals, requiring a relationship so intimate and all-encompassing that it cannot be shared with others,” the document said.
Cardinal Víctor Manuel Fernández, prefect of the doctrinal dicastery, wrote in the document’s introduction that the dicastery wanted to draw from Scripture, theology, philosophy and “even poetry” to explain why it is best to choose “a unique and exclusive union of love, a reciprocal belonging that is rich and all-embracing.”
The poets quoted included Walt Whitman, Pablo Neruda, Emily Dickinson and Rabindranath Tagore.
The dicastery said it issued the note in response to requests from the bishops of Africa where polygamy is still practiced as well as because “various public forms of non-monogamous unions – sometimes called ‘polyamory’ – are growing in the West.”
“Polygamy, adultery or polyamory are based on the illusion that the intensity of a relationship can be found in the succession of faces,” the document said. But “as the myth of Don Juan illustrates, numbers dissolve the names; they disperse the unity of the loving impulse.”
While the Church, its theologians, pastors and canon lawyers have written much about the indissolubility of the marriage bond, the note said, there has been less official reflection “on the unity of marriage – meaning marriage understood as a unique and exclusive union between one man and one woman.”
The doctrinal dicastery insisted that sacramental marriage is forever and that openness to procreation is an essential part of marriage, but it also said the purpose of the doctrinal note was to focus primarily on the unitive aspect of marriage.
While there are examples of polygamy in the Old Testament, many other passages celebrate the love found in an exclusive, monogamous relationship, it said. And the Song of Songs uses the language of a lover and beloved allegorically to refer to the relationship of God with his people – a relationship that is unique and exclusive.
In the Gospels, it said, Jesus exalts faithful, lifelong monogamy, pointing back to God’s “original plan” that a man and a woman would become “one flesh.”
The document has a long section on what popes and Christian theologians – from the early Church to modern times – have said and written about marriage.
Unlike other early theologians, it said, Saint John Chrysostom did not emphasize procreation as a primary purpose for marriage but wrote that “the unity of marriage, through the choice of a single person to whom one is joined, serves to free people from an unrestrained sexual outlet devoid of love or fidelity, and properly directs sexuality.”
Until Pope Leo XIII wrote an encyclical on marriage in 1880, the popes did not write much about matrimony, the document said.
In that encyclical, it said, the pope’s defense of monogamy was in part “a defense of the dignity of women, which cannot be denied or dishonored even for the sake of procreation. The unity of marriage therefore implies a free choice on the part of the woman, who has the right to demand exclusive reciprocity.”
Because marriage is a union between a man and a woman “who possess exactly the same dignity and the same rights,” the document said, “it demands that exclusivity which prevents the other from being relativized in their unique value or being used merely as a means among others to satisfy needs.”
In the Latin-rite sacrament of matrimony, it noted, “consent is expressed by saying: ‘I take you as my wife,’ and ‘I take you as my husband.’ In this regard, following the teaching of the Second Vatican Council, it must be said that consent is a ‘human act by which the spouses mutually give and receive one another.’”
“This act, ‘which binds the spouses to each other,’ is a giving and a receiving: it is the dynamism that gives rise to mutual belonging, called to deepen, to mature and to become ever more solid,” the doctrinal note said.
How that belonging to one another in an exclusive way is lived out may change over time, “when physical attraction and the possibility of sexual relations weaken,” the document said, but it does not end.
“Naturally, various intimate expressions of affection will not be lacking, and these are also considered exclusive,” it said. “Precisely because the experience of reciprocal and exclusive belonging has deepened and strengthened over time, there are expressions that are reserved only for that person with whom one has chosen to share one’s heart in a unique way.”
“The mutual belonging proper to exclusive, reciprocal love implies a delicate care, a holy fear of profaning the freedom of the other, who has the same dignity and therefore the same rights,” the note said.
The unique friendship of spouses, it said, is “full of mutual knowledge, appreciation of the other, complicity, intimacy, understanding and patience, concern for the good of the other and sensitive gestures.”
That friendship “ transcends sexuality,” but “at the same time embraces it and gives it its most beautiful, profound, unifying and fruitful meaning,” the document said.

