My partner and I have promised to follow biblical principles of marriage. Why should we participate in a public wedding ceremony? Why is it that our promise to each other is not acceptable?
R. C. Sproul – Because there are not any witnesses. You do not have private covenants in the Bible. Marriage is a covenant and a covenant relationship involves making promises and not making them in the back seat of a car. They are made with public witnesses.
In the traditional wedding ceremony, most start off, “Dearly Beloved, we are gathered here today in the Presence of God and of these witnesses, to unite this man and this woman in the sacred bond of matrimony” and so on.
What happens on that occasion (which is public, that makes it more than just a piece of paper) is that I have made a commitment to that woman, out loud, in front of every authority structure of my life – in front of my family, in front of her family, in front of the Church, in front of the civil magistrate, and in front of my friends. And if I break that vow, its possible that my friends won’t take it seriously, and its possible that my family won’t take it seriously, its possible that the Church won’t take it seriously, and its even possible nowadays that the State won’t take it seriously; but you’d better believe that God is going to take it seriously.
But this idea of a private covenant – just is not done in Scripture. There always has to be some kind of witness to the covenant and some kind of document or treaty.
Why was the Ten Commandments written in stone and placed in the ark of the covenant?
Because they are the stipulations of the covenant that God makes with Israel, when He unites in marriage to His people.
This is part of the absolute fall out of the radical secularization of marriage in our culture. You are kidding yourself if you think you have a marriage that is private promises.
A transcript from a Question and Answer Session at the Ligonier Ministries National Conference, Bought with a Price, Orlando, 2006
A transcript from a Question and Answer Session at the Ligonier Ministries National Conference, Bought with a Price, 
Jesus made it very, very clear that Moses, because of the hardness of their heart, gave them the right for divorce on the basis of the “unclean thing,” which is not specifically adultery but its “unclean” and so the whole debate amongst the Jewish Rabbis was, “What constitutes the unclean thing?”
Question: How do you interpret Paul’s qualification of “the husband of one wife” for a local church elder? (1 Timothy 3:2)
I think it is clear as can be, that what the issue there that Paul is addressing is polygamy. And in the Early Church in its formation, it took a while for the principle of monogamy to be firmly established within the Christian community because there were guys who had two or three or four wives (concubines) and that was opposed to biblical marriage, and if you have two wives, that’s one too many (at the same time, obviously).