It is Christ who reveals the truth about marriage - by taking man away from his 'hardness of heart' and opening him to marriage's original meaning. Then, through his death on the cross he reveals the plan of God from before time - that God has wished to unite humanity to Himself. So, married love, between two baptised people becomes an expression of this Mystery, and by which spouses are called to incarnate Christ's love in the world.
Tertullian, one of the ancient Fathers of the Church famously spoke of marriage in these words: "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."
The Catholic Church teaches that marriage between the baptised is a Sacrament. So, when two baptised people marry they are inserted into the Redeeming action of Christ's love for the Church, and are sustained and enriched by His saving power. Christ's love for the Church is unbreakable - so too is its sacrament. Spouses then, become witnesses to the Church and to their children of the saving Mystery of Christ's death and Resurrection.
Through the sacrament of marriage spouses are able to witness to the way in which God has revealed His love. Furthermore, they are able to make that love present through the manner in which they relate to each other and to their children. And, they are able to point to the full revelation of Christ's love at the end of time.
Not only does Christian marriage express the reality of Christ's love for the Church but, first it is a real communion of two persons. The spouses participate in Christ's love in real ways - through their bodies, instincts, feelings, affections, aspirations and will they bring about a unity of persons - a unity of heart and soul. In other words, all the characteristics of married love: indissolubility, fidelity, exclusivity and openness to life are given a new meaning by Christ. (FC, 13)