From Familiaris Consortio:
Jesus Christ, Bridegroom of the Church, and the Sacrament of Matrimony
13. The communion between God and His people finds its definitive fulfillment in Jesus Christ, the Bridegroom who loves and gives Himself as the Savior of humanity, uniting it to Himself as His body.
He reveals the original truth of marriage, the truth of the “beginning,” and, freeing man from his hardness of heart, He makes man capable of realizing this truth in its entirety.
This revelation reaches its definitive fullness in the gift of love which the Word of God makes to humanity in assuming a human nature, and in the sacrifice which Jesus Christ makes of Himself on the Cross for His bride, the Church. In this sacrifice there is entirely revealed that plan which God has imprinted on the humanity of man and woman since their creation; the marriage of baptized persons thus becomes a real symbol of that new and eternal covenant sanctioned in the blood of Christ. The Spirit which the Lord pours forth gives a new heart, and renders man and woman capable of loving one another as Christ has loved us. Conjugal love reaches that fullness to which it is interiorly ordained, conjugal charity, which is the proper and specific way in which the spouses participate in and are called to live the very charity of Christ who gave Himself on the Cross.
In a deservedly famous page, Tertullian has well expressed the greatness of this conjugal life in Christ and its beauty: “How can I ever express the happiness of the marriage that is joined together by the Church strengthened by an offering, sealed by a blessing, announced by angels and ratified by the Father? …How wonderful the bond between two believers with a single hope, a single desire, a single observance, a single service! They are both brethren and both fellow-servants; there is no separation between them in spirit or flesh; in fact they are truly two in one flesh and where the flesh is one, one is the spirit.”
Receiving and meditating faithfully on the word of God, the Church has solemnly taught and continues to teach that the marriage of the baptized is one of the seven sacraments of the New Covenant.
Indeed, by means of baptism, man and woman are definitively placed within the new and eternal covenant, in the spousal covenant of Christ with the Church. And it is because of this indestructible insertion that the intimate community of conjugal life and love, founded by the Creator, is elevated and assumed into the spousal charity of Christ, sustained and enriched by His redeeming power.
By virtue of the sacramentality of their marriage, spouses are bound to one another in the most profoundly indissoluble manner. Their belonging to each other is the real representation, by means of the sacramental sign, of the very relationship of Christ with the Church.
Spouses are therefore the permanent reminder to the Church of what happened on the Cross; they are for one another and for the children witnesses to the salvation in which the sacrament makes them sharers. Of this salvation event marriage, like every sacrament, is a memorial, actuation and prophecy: “As a memorial, the sacrament gives them the grace and duty of commemorating the great works of God and of bearing witness to them before their children. As actuation, it gives them the grace and duty of putting into practice in the present, towards each other and their children, the demands of a love which forgives and redeems. As prophecy, it gives them the grace and duty of living and bearing witness to the hope of the future encounter with Christ.”
Like each of the seven sacraments, so also marriage is a real symbol of the event of salvation, but in its own way. “The spouses participate in it as spouses, together, as a couple, so that the first and immediate effect of marriage (res et sacramentum) is not supernatural grace itself, but the Christian conjugal bond, a typically Christian communion of two persons because it represents the mystery of Christ’s incarnation and the mystery of His covenant. The content of participation in Christ’s life is also specific: conjugal love involves a totality, in which all the elements of the person enter- appeal of the body and instinct, power of feeling and affectivity, aspiration of the spirit and of will. It aims at a deeply personal unity, the unity that, beyond union in one flesh, leads to forming one heart and soul; it demands indissolubility and faithfulness in definitive mutual giving; and it is open to fertility (cf Humanae vitae, 9). In a word it is a question of the normal characteristics of all natural conjugal love, but with a new significance which not only purifies and strengthens them, but raises them to the extent of making them the expression of specifically Christian values.”