Marriage is ordainded of God.  Marriage was and is an inherent part of the plan of God for humankind.  No other creature on the planet has the covenant of marriage.  God himself performed the first marriage in the book of Genesis.  Also marriage is typical of the relationship that Christ has with his Church.  The Church is called the Bride of Christ , and one day he will return for his Bride who will be caught out to meet him in the Rapture.