According to the Bible, the definition of marriage is a covenant before God to fulfill the commitments that a marriage requires such as the man attending to his wife's physical and emotional needs as well as sexual exclusivity. The Bible also talks about roles within a marriage and marriage's purpose.
The Bible says that marriage is both legally and morally binding. In the book of Genesis, God says that marriage occurs between one man and one woman as an alternative to man's loneliness. However, there is some confusion in the Bible as to exclusivity of sexual relations in a marriage because several key figures in the Bible, including David and Jacob, have sexual relations with concubines. The Bible also condones the marriage of a woman captured in war against her will.
The Bible also references roles in a marriage, specifically that the husband's role is to lead the marriage, and the wife's role is to submit to the husband's authority. The purpose of Biblical marriage is to symbolically represent the covenant between God and the church. The Bible also says that marriage is a representation of a person's spiritual relationship with God.