The matrimonial covenant, by which a man and a woman establish between
themelves a partnership of the whole of life, is by its nature ordered toward the
good of the spouses and the procreation and education of offspring; this covenant between baptized persons has been raised by Christ the Lord to the dignity of a sacrament. (CCC 1601)

The sacrament of Matrimony signifies the union of Christ and the Church. It gives spouses the grace to love each other with the love whith 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.  
(CCC 1661)

Resources:
https://archseattle.org/living-catholic/marriage/