A partnership of the whole life. The sacred covenant that is marriage is not simply an agreement to exchange certain rights and duties. In marriage, "the partners mutually surrender themselves to each other (cf. "The Constitution on the Church in the Modern World," Vatican II, no. 48). This mutual giving of two persons reflects Christ’s gift of himself to us in love even to the shedding of his blood. The marriage partnership is one of total self-giving. This helps us to understand why contraception is sinful. When a married couple uses contraception, they are saying to each other, "I give you myself completely — except for my fertility. Contraception contradicts the very nature of marriage.
The good of the spouses. There are two ends or purposes to marriage. The first is the good of the spouses. Here we are speaking of spousal — or conjugal — love. There are few words that are more misused and misunderstood in our contemporary culture than "love." Popular media would have us believe that love is little other than an emotion — and a fleeting one at that — or simply physical attraction. In fact, genuine spousal love is far more.
Again, from the Catechism of the Catholic Church: "By its very nature conjugal love requires the inviolable fidelity of the spouses. This is the consequence of the gift of themselves that they make to each other. Love seeks to be definitive; it cannot be an arrangement ‘until further notice.’ The ‘intimate union of marriage, as a mutual giving of two persons, and the good of children demand total fidelity from the spouses and require an unbreakable union between them’" (1646).
But there is more. Marriage was not created by God only for the good of the spouses. There is a second — and equally important — purpose of marriage.
The procreation and education of offspring. By its very nature, marriage is ordered to the procreation of children. While not every act of marital intercourse will result in the conception of a child, every act of intercourse must be open to the gift of a child. Here, again, we see why every act of contraception is a gravely sinful. Contraception literally truncates the meaning of marriage. It eliminates one of the intrinsic purposes of marriage. "Fecundity is a gift, an end of marriage, for conjugal love naturally tends to be fruitful. A child does not come from outside as something added on to the mutual love of the spouses, but springs from the very heart of that mutual giving, as its fruit and fulfillment. So the Church, which is ‘on the side of life,’ teaches that ‘it is necessary that each and every marriage act remain ordered per se to the procreation of human life.’" (CCC 2366).
Raised to the dignity of a sacrament. Marriage as a natural institution comes from the creation as recorded in the Book of Genesis. The marriage of two baptized Christians, however, is different from marriage as a purely natural union. "The grace of the sacrament perfects the love of husband and wife, binds them together in fidelity, and helps them welcome and care for children. Christ is the source of this grace and he dwells with the spouses to strengthen their covenant promises, to bear each other’s burdens with forgiveness and kindness, and to experience ahead of time the ‘wedding feast of the lamb’" (United States Catholic Catechism for Adults, 285).
