Advocates of redefining marriage sometimes cite the Bible, pointing to the variety of marital forms in the Old Testament.
Richard Whitekettle at Public Discourse explains why not all forms of marriage in the Old Testament are equal:
While it is certainly true that marriage takes various forms in the Old Testament, and that no direct condemnations of these various forms are ever made, Robinson, Pauw, and those of like mind are missing or ignoring or dismissing one very important interpretive feature of the Old Testament: its narrative trajectory.
The Bible presents the history of the world as involving its creation (the pre-fall world), its fall, and its continuation as a fallen world (the post-fall world). In other words, the Bible understands the world to have been made in a certain way, to have fallen apart in a certain way, and to continue on in a certain fallen way.
Consider, then, the eight marital forms in light of the pre- and post-fall structure of the history of the world. The only marital arrangement found in the ideal, pre-fall world is the man + woman arrangement....
While formal deviations from the standard emerge in the fallen world of the Old Testament, a material deviation never does. It was not considered a viable, material form of marriage, even in the fallen world. Thus, while the variety of marital forms in the Old Testament cannot be used to support the notion that same-sex marriage does not deviate from a biblical norm, the common and exclusively heterosexual character of the various forms of marriage found in the Old Testament (together with the prohibition and condemnation of homosexual behavior itself in Lev 18:22 and 20:13) rules out the possibility of support even further.
Some people of faith make arguments in support of marriage based on their religious views. The scriptural narrative Whitekettle examines is important for Christians to understand so that they can be ready to address the claims that because a variety of unions are described in the Old Testament, it is somehow okay to redefine marriage.