Look what I just read from A.A. Hodge in his commentary (1869) on the Westminster Confession-
Marriage was ordained of God, and is therefore a divine institution. This is so -- (1.) Because God created man male and female, and so constituted them, physically and morally, that they are mutually adapted to each other and are mutually helpful to each other under the law of marriage, and not otherwise; and (2.) Because the law of marriage, the conditions of its contract, continuance and dissolution, are laid down in the Word of God.
Hence it follows that marriage is a religious as well as a civil contract. No State has any right to change the law of marriage, or the conditions upon which it, may be lawfully constituted or dissolved, as these have been ordained by God. Neither has any man or woman a right to contract any relation different in any respect, as to its character or duration, from that which God has ordained as marriage. Hence marriage is a human contract under the limits and sanctions of a divine constitution, and the parties contracting pledge their vows of truth and constancy to God as well as to each other and to society.
But it is also a civil contract, because every State is bound to protect the foundations upon which social order reposes, and every marriage involves many obvious civil obligations and leads to many civil consequences touching property, the custody of children, etc. The State must therefore define the nature and civil effects of marriage, and prescribe conditions upon which and modes in which it shall be publicly acknowledged and ratified or dissolved. It is of the highest importance that the laws of the State do not contravene the laws of God upon this subject, but be made in all respects to conform to them.