Opponents of marriage equality often appeal to the Bible to support their views. So what is this "biblical standard for marriage" we keep hearing about? Marriage in the Bible is not restricted to one man and one woman, or in fact to any one model. There is, however, a unifying theme to the diverse pictures of God-ordained marriages in the Bible, and it is that different kinds of unions are accepted in different places and times, evolving in tandem with broader cultural shifts.
This is not as shocking as it may first seem to more conservative readers of Scripture. Precisely the same principle is recognized in other areas. Consider the admonition against women braiding their hair, and the prohibition against women teaching (in any capacity!), which are generally understood to be culturally specific (1 Timothy 2:9-12). The oft-cited statement that a church overseer should be "the husband of one wife" comes three verses after these other culturally bound instructions (1 Timothy 3:1-2).
Marital guidelines in the New Testament are clustered with instructions on other types of relationships elsewhere as well. The passage in Ephesians that assumes a normative husband-wife relationship (and a hierarchy within it) is followed five verses later by the directive to slaves to obey their masters (Ephesians 5:22-33, 6:5-9). The similar marriage text in 1 Peter comes on the tail of a command to slaves to submit to their masters, this time with the addition, "not only to those who are good and gentle, but also to those who are perverse" (1 Peter 2:18, 3:1-7). There is no logical reason to read one set of instructions as culturally bound and the other as universal. This is an interpretive choice that begins with a reader's notions about marriage and slavery and ends with a view of Scripture -- not the other way around.
In his instruction to wives to be submissive, Peter turned to his Scriptures (the Hebrew Bible) for authority. As he explains, "in former times the holy women" used to submit to their husbands, as "Sarah obeyed Abraham, calling him lord" (1 Peter 3:5-6). Since this is the biblical model to which Peter turns, we might benefit from looking at it ourselves.
Sarah was Abraham's half-sister (Genesis 20:12). "Well, that's not his point," one might say. Exactly: who the two parties were in relation to one another was not his point. It was, however, a central point for them. At that time in ancient Israel, the ideal marriage was within the family. This is why Abraham sends his servant to find Isaac a wife from among his kin, and God blesses Isaac with Rebekah, his first cousin's daughter (Genesis 24:4, 15). In the next generation, Isaac tells Jacob to marry from among his cousins (Genesis 28:2), and he does -- two of them. Jacob's brother Esau, on the other hand, marries outside of his family, and this is seen as a less good choice; Esau then alleviates the situation by additionally marrying his first cousin (Genesis 26:34-35, 28:8).
But as we might agree, Peter's point was not actually to uphold the biblical standard for marriage between close relatives. He upheld the Scripture itself, but understood that this model for who the parties should be -- which was utterly central in its original setting -- was not applicable in his cultural context.
In a similar vein, the Bible reflects a range of perspectives on mixed marriages from different historical settings. One part of the Torah says that no Moabite may become a part of Israel (intermarriage being a primary way for this to happen), or their descendents, even to the 10th generation (Deuteronomy 23:3). The books of Ezra and Nehemiah prohibit all mixed marriages, also naming Moabites in particular (Ezra 9-10, Nehemiah 13:1-3, 23-31). In the book of Ruth, though, the heroine is a Moabite woman who marries an Israelite man, becomes part of Israel and her great-grandson is King David (that would be her descendent to the third generation). In Ruth, there is no objection to this at all -- in fact, the only obstacle the couple must overcome is that a closer relative has the right to "acquire" Ruth first if he wishes. Those who would like simply to erase the prohibitions of Ezra and Nehemiah by superimposing Ruth must grapple with this: the story shows an acceptance of intermarriage, but it simultaneously upholds the biblical law requiring the widow of a childless man (such as Ruth's late husband Mahlon) to marry and reproduce with his closest possible kin, unless he refuses and a certain ritual involving a sandal is performed (Deuteronomy 25:5-10, Ruth 4:3-9). This complicated scenario reflects the priority of insuring the late husband's family line and inheritance. In the particular historical setting of Ruth, unlike some others in the Bible, this was the standard for marriage that met the needs of society.
Ezra and Nehemiah's adamant prohibitions against mixed marriage were intended to protect both sanctity and society at a time when the stability of Israel was in question (during the restoration of Judah after return from the Babylonian exile). These two great leaders and proponents of the Torah of Moses were not concerned with the fact that the prohibition would have incriminated Moses himself, who had married a Midianite (Exodus 2:16-22). Such prohibitions could be read as universal and applicable today, to discriminatory and destructive ends, as they were not too many decades ago. Here again we see two principles at work: that biblical mandates for marriage shifted according to perceived cultural needs, and that the interpretive choice of what is seen as applicable today begins with the reader's preconceived notions before ever opening the Bible.
Each of these biblical standards for marriage -- polygamy, marriage within the family, reproduction with a late husband's closest kin, prohibitions against intermarriage -- were seen as vital in some historical contexts as reflected in the Bible, and not in others. In times and places where marriage to a first cousin was the ideal, the Bible says such marriages are blessed by God. When polygamy was the cultural norm, that too is said to be blessed (as God blesses Jacob's marriages with the sisters Rachel and Leah, as well as with their slaves; Genesis 30). Kinship and property are important factors in many biblical marriages; one element that rarely figures into biblical standards for marriage, however, is love.
Marriage in the Bible is also not restricted to couples who can reproduce together biologically. Some biblical couples do not have children; others use a surrogate, such as Abraham and Sarah (Genesis 16), Jacob and Rachel, and Jacob and Leah (Genesis 30). In the latter two cases, each sister explicitly claims her surrogate's babies as her own, and all are presented as given by God.
So is it down to the garden of Eden, then? Adam and Eve never actually got married. If a woman created as an adult from a man's rib (and then called "his woman" or "his wife" -- this is the same word in Hebrew) is our example of what marriage should look like, good luck to us all. It is no more logical to see the Eden story as establishing that all spouses in the world should be male and female than as establishing that all people should till the soil.
Some point to Adam and Eve as the authoritative model because Jesus refers to them in Mark 10:1-12. The context is this: Jesus has been asked whether it's lawful for a man to divorce his wife, and he answers by citing the Eden story and says, "Therefore, what God has joined together, let no one separate." He adds -- and this is the clearest statement about marriage that Jesus makes -- that anyone divorced and remarried is committing adultery. The logic behind reading this as the authoritative statement about heterosexuality and not about divorce or remarriage is, shall we say, questionable. Notably, it's hard to find too many heterosexual married people (including those who appeal to the Bible in opposition of gay marriage) who argue that divorce and remarriage should be illegal.
While the traditional view is that the Bible sets standards, and cultures either follow these standards or don't, the Bible itself shows us that cultural norms and biblical positions shifted in tandem. This does not mean that anything goes; it's simply what we see in the biblical texts themselves. It does not mean that there are no standards; there were always incest taboos, for example, but what counts as incest is culturally dictated, and our society does not embrace many biblical perspectives on this (e.g., the ideal of marrying one's first cousin). It does not mean that God is a pushover; it shows, if anything, a God who will engage people in the world in which they live.
The variety we see in biblical models of marriage cannot be brushed off as a development from the Old Testament to the New Testament. Peter uses the half-siblings Sarah and Abraham as his ultimate model of marriage, Jesus views divorce and remarriage as adultery, and Paul says it's better not to marry at all, but allows it "as a concession" (1 Corinthians 7:1-6). Ruth the Moabite, meanwhile, had married an Israelite and brought King David into the world, and according to the New Testament, his descendent Jesus.
Marriage in the Bible is not restricted to one man and one woman. The biblical models for marriage include a range of relationships and combinations, and these evolve with the culture.