Isaiah asks, I was wondering what constitutes a biblical marriage. From my understanding, it is sex that makes a man and woman married in God’s eyes. Therefore, how is sex outside of legal marriage a sin?
The Bible does not give un any instructions on how to perform a wedding ceremony. The very marriage between Adam and Eve was performs by God Himself. He simply declared them to be husband and wife. In fact, there is no description of a marriage ceremony at all in the Bible.
That said, the belief that sex is what makes a marriage in God’s eyes is a completely backwards view of God’s vision for marriage.
God makes clear that marriage comes first and is followed by intimacy. He made Eve for Adam as his partner before they were joined together.
Jesus says in Matthew 19 that “a man shall … hold fast to his wife” and only after that shall “the two become one flesh” (verse 5). The identity as “husband” and “wife” come before the consummation of that union.
The author of Hebrews presents the clearest case for marriage as the place for sexual relations, saying “Let the marriage bed be undefiled, for God will judge the sexually immoral and adulterous” (Hebrews 13:4). From this, we see that sexual immorality does not just include cheating on a spouse with another person, but also includes sexual relations with anyone who is not your spouse.
Sex is a gift from God given to people inside the covenant of marriage. Marriage provides the place for sex; sex does not make a marriage.
Since we don’t have a biblical example for what constitutes marriage in society—although the Bible does include many principles for married people—we believe that Christians should follow the laws where they live. Here in America, that usually involves a legal contract in the form of a license. In other parts of the world, it might be different. But Christians should enter into a marriage that is recognized as an official marriage. Only then is sex not a sin.