Why does the Bible mainly focus on women committing adultery? Numbers chapter 5 describes a purity ceremony that determines if the wife cheated, but there is no equivalent for men. It may be that the classification of adultery differs under a polygamous system.
Num 5:25 “The priest will take the jealousy offering from the woman’s hand, lift it up before the Lord, and carry it to the altar. 26 He will take a handful of the flour as a token portion and burn it on the altar, and he will require the woman to drink the water. 27 If she has defiled herself by being unfaithful to her husband, the water that brings on the curse will cause bitter suffering. Her abdomen will swell and her womb will shrink, and her name will become a curse among her people. 28 But if she has not defiled herself and is pure, then she will be unharmed and will still be able to have children.
Envy is a sin, so this “jealous offering” was mainly designed to protect women from false accusations by jealous husbands. It was adultery for a man to sleep with another man’s wife. In contrast, if a married man sleeps with an unmarried woman, it could count as fornication, and he would be penalized to pay the bride price for her family and possibly marry her as a second wife. Essentially, a man could just marry a mistress as a second wife if he could afford it. A man (no distinction between married or unmarried is made in the text) who fornicates with an unmarried woman would pay the bride price, and if the father permits, he would marry her (Ex 22:16-17), and he can’t divorce her (Deut 22:28-29).
This means if a polygamous man has sex with an unmarried woman, it was fornication, not adultery. So when Abraham used Hagar as a surrogate in Genesis 16, it was sinful because of his lack of faith and his sexual abuse of a slave, and there is no indication that he married her. It was not technically adultery the way we think of it today. Meanwhile, King David had at least eight wives (2 Sam 3:3-5, 2 Sam 5:13-16, 2 Sam 11:26-27) and at least 10 concubines (2 Sam 15:16, 2 Sam 5:13). However, it counted as adultery with Bathsheba because she was another man’s wife. Then he had the man killed and married her (2 Sam ch.11).
In Genesis 17, God makes it clear that all of Abraham’s children will be blessed (he promised a blessing for Ishmael in the previous chapter), but only the one who comes from Sarah (his first wife) will be the promised seed. Abraham has eight children, one with Hagar, one from Sarah, and six more after Sarah dies with his new wife, Keturah (Gen 25:1-5). God’s promised seed was Isaac (Sarah’s son) and indicated that with the name change of Sarah (Gen 17:15-22), no one else. This shows that God favors monogamy, and even Isaac is monogamous in his marriage. Notice that Abraham never took another wife during the entire time Sarah was alive and barren? We met him at the age of 75, and he remained monogamous throughout that time. Hagar was just a one-time thing. Even with Abraham’s deceptive habits concerning his wife, God prevents the Pharaoh and King Abimelech from sleeping with Abraham’s wife (Genesis 12:10-20, Gen 20:1-18), God secures his covenant with Abraham to prevent him from screwing it up by actively protecting the sanctity of his marriage. This means God disapproved of Abraham giving away his wife, putting her in near-adulterous situations, which is why He intervened. In addition, he did not acknowledge his abuse of Hagar, which is why, in Genesis 17:1, God instructed Abraham to “Serve me faithfully and live a blameless life” after the Hagar situation. Abraham failed multiple times, but God showed mercy and stayed faithful to His promise.
In most Abrahamic religion-based cultures today, polygamy is limited to four wives since Jacob had only four wives, but this limitation is not explicitly written in the Old Testament. Jacob stopped at four wives because his father-in-law required it as part of their covenant (Gen 31:48-50). So under that principle, there could be a limit set by the fathers of one of the wives, and committing adultery would mean adding more wives since that is breaking the specific covenant set with the wives one has. While polygamy was permitted in the Bible in the Old Testament, it was never endorsed as a good idea, and kings and priests were prohibited from engaging in it (Deut 17:16-17).
In the New Covenant, however, men are told to have one wife (1 Tim 3:2), mimicking Christ’s relationship with the one church (body of Christ). Polygamy was allowed in the Old Testament because there was only one group of covenant people (the Israelites), and their goal was to preserve until the Messiah came. In the Old Covenant, more covenant people were made by having more physical children through reproduction, as this covenant is built on blood relations to Abraham—one way to ensure that one’s line carried on was to have more than one wife. This also allowed for the practice of Levirate marriages, which is when a widow marries her deceased husband’s male relatives to produce an heir, as seen in the Book of Ruth. If a widow wants to marry a male relative, but he is already married, polygamy allows the marriage to happen anyway, so that the land inheritance has a chance of being passed on. However, there were grievous consequences and familial strife caused in these kinds of relationships, as they are not the original model set up in Genesis 2:24. This is why, in the New Covenant, making more covenant people is accomplished by sharing the gospel, so that people are born again in the Spirit. Therefore, marriage is not necessary or valid in fulfilling the Great Commission.
Under a monogamy framework, it is adultery for a married (man or woman) person to sleep with anyone other than their spouse, and this is for both men and women. This is the framework that God established in the beginning, as described in Genesis 2:24, and Jesus quotes it in Matthew 19:4. Furthermore, Paul writes that church leaders should have only one wife (1 Timothy 3:1-6). Therefore, Christian men who lust after other women are adulterers. Jesus affirms this in Matthew 5:27-30.
Matthew 5:27 (NLT) 27 “You have heard the commandment that says, ‘You must not commit adultery.’ 28 But I say, anyone who even looks at a woman with lust has already committed adultery with her in his heart. 29 So if your eye—even your good eye—causes you to lust, gouge it out and throw it away. It is better for you to lose one part of your body than for your whole body to be thrown into hell. 30 And if your hand—even your stronger hand—causes you to sin, cut it off and throw it away. It is better for you to lose one part of your body than for your whole body to be thrown into hell.
For a Christian who was already in a polygamous marriage before getting saved, I don’t believe they must divorce their wives, simply because they are now Christians, because that would be cruel since wives are dependent on husbands in those cultures, but they shouldn’t seek to accumulate anymore. Otherwise, he is committing adultery if he is breaking his contract with his current wife. Learn more about Biblical Polygamy here.