In marriage we are called to imitate the self-giving, fruitful love of God in a lifelong union marked by charity and fidelity. Marriage was created by God for a dual purpose, which is described in paragraph 8 of the document:
"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. "Through marriage, then, we not only prepare one another for heaven, but participate as co-creators (in the case of biological parenting) and co-redeemers (in the case of adoptive parenting) in the formation of those young souls.
By "co-redeemers," I am not suggesting that adopted children are more flawed or sinful than children raised by their natural parents (it is not their fault that their parents are unable to care for them). Rather, adoption is the process by which a child who cannot be raised according to the natural order (in the loving embrace of their natural parents, a man and woman joined for life in the sacrament of matrimony) can begin to experience in his or her adoptive family the love and security that is the natural right of every child.
In one sense, adoption is never God's first choice for a child. He set the universe to run according to certain principles, called "natural law," and when that plan is disrupted suffering is inevitable. Sadly, it is often the child who suffers most. This suffering is compounded for couples who are unable to conceive, who must grieve and reconcile themselves to the reality of their situation. In both cases, adoption is no magic pill, and cannot wipe away the circumstances that made the adoption necessary.
And yet, love is the most powerful force in the universe. When we choose to open ourselves to that love, and to imitate that love the God who adopted us as His children (see Galatians 3:25-4:7), we begin the process of healing that leads us closer to the perfection God always intended.