"On their wedding day, the couple says a definitive "yes" to their vocation of marriage. Then the real work of marriage begins. For the remainder of their married lives, the couple is challenged to grow, through grace, into what they already are: that is, an image of Christ‘s love for his Church." - Marriage: Love and Life in the Divine Plan, United States Conference of Catholic Bishops
The doctrine of "Theology of the Body" is related to the sacramentality of Christian marriage, contained in Humanae Vitae, by Pope Paul VI and confirmed in Pope John Paul II's Apostolic Exhortation Familiaris Consortio, fruit of the 1980 Synod of Bishops on "The Role of the Christian Family," Read a short overview of the Theology of the Body here.