8 Married love particularly reveals its true nature and nobility when we realize that it takes its origin from God, who "is love," (6) the Father "from whom every family in heaven and on earth is named." (7) Marriage, then, is far from being the effect of chance or the result of the blind evolution of natural forces. It is in reality the wise and provident institution of God the Creator, whose purpose was to effect in man His loving design. As a consequence, husband and wife, through that mutual gift of themselves, which is specific and exclusive to them alone, develop that union of two persons in which they perfect one another, cooperating with God in the generation and rearing of new lives. The marriage of those who have been baptized is, in addition, invested with the dignity of a sacramental sign of grace, for it represents the union of Christ and His Church.
Source: Humanae Vitae (Vatican.va)