"Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh."  
Genesis 2:24

1661 The sacrament of Matrimony signifies the union of Christ and the Church. It gives spouses the grace to love each other with the love with which Christ has loved his Church; the grace of the sacrament thus perfects the human love of the spouses, strengthens their indissoluble unity, and sanctifies them on the way to eternal life (cf. Council of Trent: DS 1799).

2365 Fidelity expresses constancy in keeping one's given word. God is faithful. The Sacrament of Matrimony enables man and woman to enter into Christ's fidelity for his Church. Through conjugal chastity, they bear witness to this mystery before the world. 

1623 According to Latin tradition, the spouses as ministers of Christ's grace mutually confer upon each other the sacrament of Matrimony by expressing their consent before the Church.