One of the ideal goals of life held up by Christianity is that of a "biblical marriage." This is a monogamous marriage between one man and one woman, usually seen as a loving and caring union. It receives the adjective "biblical" to clarify that the Bible approves of this form of marriage. This is accurate, but not the entire story.
The Bible approves of many different forms of marriage, some of which our society would find abhorrent or even criminal. A few of these relationships meet our understanding of a formal marriage, but others are approved relationships short of formal marriage, but which include sexual congress. Sometimes it is hard to tell which is which.
One of the most common forms of marriage in the Bible is polygyny, one man joined to two or more women. This may be a formal situation in which the man is legally wedded to each woman. Both King David and King Solomon had several formal marriages, sometimes to quite important women. For example, Solomon married a daughter of a Pharaoh, the most powerful ruler in the region.
Polygyny also takes place when one or more of the women are simply part of the household, often slaves. For example, Abraham's first son, Ishmael, was born from his wife's slave, Hagar, while Jacob had children with both Bilhah and Zilpah, the slaves of his two official wives.
Slavery is often the context for different types of marriage. Exodus 21 alone discusses four ways in which the slavery of women is the basis for union. An adult male who buys a female slave may enter into a relationship with her himself, either as his sole female partner or alongside an official wife. The master may also designate the woman as an official wife for his son, or as a partner for one of his male slaves.
Another widely known form of biblical marriage is the Levirate Marriage. In this case, if a married man dies childless, the widow is required to marry his brother (Deuteronomy 25) or a close relative (Ruth 4). The first son of the new union is treated as the dead man's heir. The surviving brother or relative may reject such a marriage, but the widow may not.
Then there is the case of a rapist in Deuteronomy 22:28-29. A man who rapes an unbetrothed virgin must marry his victim and is never allowed to divorce her. The woman has no choice in the matter.
Finally, a soldier who captures a "beautiful woman" while he is plundering an enemy's dwelling may bring her home and force her to marry him. Deuteronomy 21:10-14 puts a couple conditions on this marriage, including the right of the captive to mourn her parents, who presumably had been killed in the raid. Despite this caveat, this is essentially rape.
In modern America, Christianity, Judaism and our secular society view most of these unions as neither valid forms of marriage nor acceptable types of human relationships.
The rejection of these biblically approved types of marriage in favor of only monogamous marriage indicates that even Christians, who believe that the Bible is the basis for guiding their life, pick and choose which aspects of the Bible they will follow. In other words, all Scripture may be sacred, but not all Scripture is relevant, or even correct.
It is our modern sense of justice to both men and women that denies validity to these forms of marriage. We outlawed slavery more than a century and a half ago. We understand the trauma that rape brings upon a woman; permanently linking a woman to her rapist is just unthinkable.
The reason we view these ideas of marriage as invalid is that our society holds different concepts of men's and women's inherent nature, and we have different notions of what they need for successful and happy lives. Attempts to map our modern practices back onto the Bible fail, as shown here, because the social world imagined by the Bible has long disappeared.