From A Christian Declaration on Marriage

This statement is endorsed by the ACA

We believe that marriage is a holy union of one man and one woman in which they commit, with God’s help, to build a loving, life-giving, faithful relationship that will last for a lifetime. God has established the married state, in the order of creation and redemption, for spouses to grow in love of one another and for the procreation, nurture, formation, and education of children.

The Scriptural basis for the above statement has been accepted for centuries and need not be reviewed here, but recent civil actions and court rulings reveal a fundamental lack of understanding of the nature of marriage in our time.

The Creator of all things established the marital partnership as the foundation of human society. Accordingly, marriage is by divine ordinance and by its very nature a constituent and a sacrament of community, and the basis of a sound society. This bond, then, which is essential for the good of the married parties, of their children, and of society itself, does not depend upon the "private choice" of the partners alone, but is inherently social and communal. It is for this reason that human societies everywhere and at all times have established institutions to promote the dignity, prosperity, peace and well-being of the family.

By their very nature, marriage and married love are ordained for the procreation and subsequent nurture of children, as well as for mutual comfort and support. Thus marriage can exist only between one man and one woman in an exclusive, lifelong union. Other relationships can and do exist - some innocent and some blameworthy - but whatever they are, they are not marriage.

Municipalities, states, countries and other political entities can choose to enact statutes attempting to contradict these truths. To do so can establish only their legal autonomy, not their rectitude or their wise policy. To defy nature and truth will always carry a price over time. When one jumps off a high structure, nothing very bad happens for a number of seconds - just enough time for the unwise to revel in soaring with the birds. What our society needs now is the wisdom and humility to abandon our childish willfulness, and to submit to what our Maker has ordained for us.

The issue is much more than a conflict between God-based and purely secular definitions of marriage. Even many who take no position on the sinfulness of the recent perversion of marriage recognize it as problematic.

Highly recommended reading: Same-Sex 'Marriage' and the Persecution of Civil Society, by Dr. Jennifer Roback Morse, author of Love and Economics: It Takes a Family to Raise a Village.