Sacrament of Matrimony

The matrimonial covenant, by which a man and a woman establish between themselves 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.
Catechism of the Catholic Church 1601

The intimate community of life and love which constitutes the married state has been established by the Creator and endowed by him with its own proper laws...God himself is the author of marriage. The vocation to marriage is written in the very nature of man and woman as they came from the hand of the Creator. Marriage is not a purely human institution despite the many variations it may have undergone through the centuries in different cultures, social structures, and spiritual attitudes. These differences should not cause us to forget its common and permanent characteristics. Although the dignity of this institution is transparent everywhere with the same clarity, some sense of the greatness of the matrimonial union exists in all cultures. The well-being of the individual person and of both human and Christian society is closely bound up with the healthy state of conjugal and family life. 
Catechism of the Catholic Church 1603

"Marriage love is above all fully human, a compound of sense and spirit. It is not, then, merely a question of natural instinct or emotional drive. it is also, and above all, an act of free will, whose trust is such that it is meant not only to survive the joys and sorrows of daily life, but also to grow, so that husband and wife become in a way, one heart and one soul, and together attain their human fulfillment. 

It is a love which is total--that very special form of personal friendship on which husband and wife generously share everything, allowing no unreasonable exceptions and not thinking solely of their own convenience. Whoever really loves his partner loves not only for what he receives, but loves that partner for the partner's own sake, content to be able to enrich the other with the gift of himself.

Married love is also faithful and exclusive of all others, and this until death. Married love is fecund. It is not confined wholly to the loving exchange of husband and wife. Marriage and conjugal love are by their nature ordained toward the procreation and education of children. Married love, therefore, requires of husband and wife the full awareness of their obligations in the matter of responsible parenthood. 

Let Christian husbands and wives be mindful of their vocation to the Christian life, a vocation which, deriving from their Baptism, has been confirmed anew and made more explicit by the Sacrament of Matrimony. For by this sacrament they are strengthened and, one might almost say, consecrated to the faithful fulfillment of their duties. For the Lord has entrusted to them the task of making visible to men and women the hoiness and joy of the law which united inseparably their love for one another." (Excerpts from Humane Vitae, Pope Paul VI)