In addition to the Scriptures, I have also looked at history, at culture, and into the writings of others on the subject. In order for a working definition of marriage to be accurate, it must be universal. I covered this in an earlier post, but I will repeat it here because it is important to my conclusion. A marriage must be a marriage in every time, in every country, in every culture, or else it isn't a marriage in any. An accurate definition of marriage can be held up to any putative marriage and everyone should be able to conclude whether the relationship we are examining IS or IS NOT a marriage. There should be no question. This would include the first marriage, of Adam and Eve, and the marriages of tribal people, modern western people, and even the marriages formed under the auspices of pagan religions.
I would also like to address the question, "Why does this matter?" It matters because God has said that the transgression of His Law is sin. As believers, we are to purify ourselves, we are to repent of sin and to walk in righteousness. In order to do that, we must be able to identify sin and righteousness. In addition, since God has declared that marriages are created as a picture of the relationship between Christ and the Church, if we have an inaccurate view of marriage, we are lying about the gospel. God has said, "Thou shalt not commit adultery." God regulates sexual activity and He has stated the only place that sexual relations are permitted is within marriage. All sexual relations outside of marriage violate His command. This means that we must know whether we are in a marriage or not, and in terms of dealing with sin in the church and the greater community, we must know if other people are in marriages or not.
So here it is, my working definition of marriage:
A life-long union between a man and woman which has been publicly declared and sexually consummated, and where the union is not otherwise prohibited by the Law of God.
It has 5 elements which can be compared to any alleged marriage to see if it is, in fact, a marriage. Firstly a marriage is to last for the entire life of either the husband or wife. In some marriage ceremonies we hear the words, "For as long as you both shall live." Marriages do not extend beyong the death of one of the parties, they don't last into heaven, but neither can they be temporary, ending before the death of one of the parties.
In the past it would have seemed silly to mention that one party to a marriage needs to be a man and one needs to be a woman, but recent history requires me to assert that if this second element is not present, there is no marriage. This is true because God specifically ordained the sexes for marriage at the time He instituted marriage and also because God has prohibited sexual relations between those of the same sex in His Law.
The third element is a public declaration. There is no such thing as a secret marriage. Violating a marriage can be a death penalty offense, so those who are married have a duty to the rest of the world to hold themselves out as married.
The fourth element is sexual consummation. Husbands and wives are not mere roommates, they are sexual partners. There is no such thing as a platonic marriage. We also need the fifth element, where no marriage can exist contrary to the Law of God because God has specifically forbidden certain people from marrying each other, even if they meet all the elements, such as mothers and sons.
Some people would try to add other elements or place other types burdens on the simplicity of marriage, but that becomes problematic when questions start to be asked, such as, "Were Adam and Eve married?" "Are people who were forced into marriages really married?" "How can we determine if the people in our church who are living together and/or having sex are actually married?"
This simple definition of marriage also makes it easy to distinguish between a man and woman who are betrothed (covenanted to marry) and a man and woman who are married.