There are three primordial covenants.
The first covenant is that of body and soul; the most intimate union. This union we protect through the directive, “do not kill.”
The second covenant is between parent and child. This is the bed rock of human community.
The third is that of man and wife.
These three covenants carry with it the warning “what God has joined man must not divide.” And their inter relatedness is expressed beautifully in Genesis when it says “a man leaves his mother and father and clings to his wife and the two of them become one flesh.” The relationship of marriage is like the relationship of parent to child and body to soul.
These primordial relationships form the natural institution of the family. This primordial institution is the foundation of the institution of the state and of religion. Religion seeks to elevate, redeem, and celebrate these primordial covenants and the state seeks to protect them and build them up.
In the recent discussions on same sex unions, the state, and religious freedom a certain power play is going on. Throughout history there has been this tug of war between the state and religion, and it was for this reason that the founding Fathers of the United States sought to protect these realms of influence through a philosophy of the separation of Church and State. However, throughout history there have also been power plays between the state and the family (and religion and the family). We can see examples of this in the one child policy of China and state restrictions on home schooling.
Now, the boundaries between three institutions are not absolute. All three are codependent and therefore must continually be in healthy dialogue with each other. For example, sometimes the state has to intervene in unhealthy family relationships.
However, same sex marriage is the ultimate power play of the state over the family. This is because the state not only claims the right to redefine marriage, but it now claims the right to redefine the family. Through same sex marriage the state nullifies all special claims of Fatherhood and Motherhood. Any special preference for motherhood and fatherhood is now discrimination. If an adoption facility prefers to give the child to a mother and father over a same sex couple that is now discrimination. If a child prefers a mother and father over a same sex couple that is now a perverted attitude and they will have to be reeducated, taught how to get over it.
Ultimately it leads to the homogenization of all relationships, even the relationship of man and wife, to the same level under an absolutism of the state. Taken to its extremes, the state can now arbitrarily redefine which relationships would be the right one for children. It is the ultimate state take over.
In abortion we saw the state divide body and soul; in divorce we saw the state divide man and wife; in same sex unions we see them separate mother from child.
(for a more extensive discussion on same sex marriage follow this link)