I was recently confronted with a challenge about marriage at one of my events. The claim was that God permits same-sex marriage today because marriage is not clearly defined in Scripture. Adam and Eve were a monogamous heterosexual couple, but later in Scripture God allowed men to marry multiple women. This signals a trajectory in the Bible towards more openness of sexual expression and in the definition of marriage. Therefore, same-sex marriage should be allowed by Christians today.
I don’t think the Bible permits same-sex marriage for a whole host of reasons, but I’ll only explain the ones I offered in response to this challenge. First, although God tolerated polygamy during Old Testament times, He never condoned it. In fact, when marriage begins in the Genesis creation account, it’s instituted as a monogamous and heterosexual relationship (Gen. 1:27–28; 2:24). That the patriarchs and other Old Testament figures practiced polygamy is not evidence that God intended them to do so. That’s just what they did. The same could be said of divorce. God never intended married couples to divorce, but He tolerated it. Even Jesus said that divorce was permitted because of the hardness of the hearts of men. Yet, He also clearly reminds the Pharisees that divorce was never intended by God from the beginning (Matt. 19:8). Therefore, when it comes to polygamy (and divorce), Scripture is descriptive but not prescriptive.
Second, even if God made provision for polygamy in the Old Testament, the 613 commands of the Mosaic Law are no longer binding on the New Testament believer. They are part of the Old Covenant (or contract) that has been replaced. Jesus said He “came to fulfill” the Mosaic Law and its requirements because we never could (Matt. 5:17). He didn’t merely abolish that covenant, however. He established a new covenant in His blood. In fact, the entire book of Galatians is an argument against making the Mosaic Law binding on believers living under the New Covenant of Christ.
Third, even if God had ordained polygamous marriage throughout all of Scripture (which I don’t believe He did), it doesn’t follow that He affirms same-sex marriage. Polygamy is fundamentally different from same-sex marriage. When a man marries a woman, he meets the male-female requirement of biblical marriage (Gen. 1:27–28 and 2:24). If he marries another woman, that is also a heterosexual marriage. Every instance of an additional marriage is still an opposite-sex marriage. It’s not same-sex marriage because the women he’s married to are not married to each other. It’s also not group marriage because he and all the women are not married together as a group. Marriage remains an opposite-sex relationship between two people as God defined in His Word.
Fourth, contrary to the claim that the Bible’s trajectory is towards greater openness in sexual expression (and consequently more openness in marriage), it seems the opposite is true. The trajectory in Scripture, especially with Jesus, is towards greater restriction. God may have tolerated polygamy in the Old Testament, but we don’t see it permitted during New Testament times. The pastoral epistles, for example, mandate that a church leader be a man of one wife (e.g. Tit. 1:6; 1 Tim. 3:2, 12). Jesus also cites several Mosaic laws and, far from loosening their prohibitions, makes them more restrictive. For example, He says, “You have heard that it was said, ‘You shall not commit adultery’; but I say to you that everyone who looks at a woman with lust for her has already committed adultery with her in his heart” (Matt. 5:27–28). Jesus takes a Mosaic prohibition and makes it more restrictive.
Fifth, the New Testament specifically rules out same-sex marriage by prohibiting homosexual sex. Although this is explicitly taught in Romans 1:26–27, 1 Corinthians 6:9, and 1 Timothy 1:10, Paul’s epistle to the Romans contains the clearest condemnation. Within the context of a creation narrative (beginning at Rom. 1:18), Paul argues that God made men and women to function in a heterosexual way. Women, he says, exchanged the natural sexual function of a man for unnatural sex with women. Men, in the same way, abandoned the natural sexual function a woman provides and had unnatural sex with other men (Rom. 1:26–27). By prohibiting same-sex sexual contact, Scripture rules out same-sex marriage.
Finally, we should give Jesus the last word on this question. Our King specifically ruled out same-sex marriage by upholding the male-female prerequisite of marriage taught in the Genesis account of creation. When asked about divorce, Jesus replies,
Have you not read that He who created them from the beginning made them male and female, and said, “For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh”? So they are no longer two, but one flesh. What therefore God has joined together, let no man separate. (Matt.19:4–6)
Notice Jesus quotes the two Genesis texts that affirm the binary nature of the sexes and the male-female prerequisite of marriage (Gen. 1:27–28; 2:24). That’s because He believes those texts are still authoritative and that marriage is still what’s described in them. Then Jesus adds his own commentary on the passage (“What therefore God has joined together…”), indicating He believes God instituted monogamous and heterosexual marriage.