Marriage has a unique place because it speaks of an absolute faithfulness, a covenant between radically different persons, male and female; and so it echoes the absolute covenant of God with his chosen, a covenant between radically different partners.
John Paul II
The communion of love between God and people, a fundamental part of the Revelation and faith experience of Israel, finds a meaningful expression in the marriage covenant which is established between a man and a woman.
For this reason the central word of Revelation, “God loves His people,” is likewise proclaimed through the living and concrete word whereby a man and a woman express their conjugal love. Their bond of love becomes the image and the symbol of the covenant which unites God and His people. And the same sin which can harm the conjugal covenant becomes an image of the infidelity of the people to their God: idolatry is prostitution, infidelity is adultery, disobedience to the law is abandonment of the spousal love of the Lord. But the infidelity of Israel does not destroy the eternal fidelity of the Lord, and therefore the ever faithful love of God is put forward as the model of the faithful love which should exist between spouses…
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….
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.