Question: "If a man has multiple wives and becomes a Christian, what is he supposed to do?"
Answer: Since polygamy is frowned upon in most societies, this is not a question too many people think about. But there are still numerous places in the world where polygamy is accepted. Many Muslim countries allow polygamy. For a man to have multiple wives is somewhat common in several African nations. Even in the United States, there are some communities that endorse polygamy. However, virtually all Bible scholars agree that polygamy is not for Christians (see Why did God allow polygamy / bigamy in the Bible?). What, then, should a polygamist do if he places his faith in Jesus Christ and becomes a Christian?
Most people immediately give an answer like “he should divorce all of his wives but one.” While that seems to be an ethical solution, the situation is usually not quite that simple. For example, which wife does he keep? His first wife? His last wife? His favorite wife? The wife that has borne him the most children? And what about the wives he divorces? How do they provide for themselves? In most cultures that allow polygamy, a previously married woman has very little opportunity to provide for herself and even fewer possibilities of finding a new husband. And what happens to the children of these wives? The situation is often very complicated. There is rarely a simple solution.
We do not believe polygamy is something God approves of in this era. However, the Bible nowhere explicitly gives a “thou shalt not marry multiple wives” command. In the New Testament, a polygamist is ineligible for church leadership (1 Timothy 3:2, 12; Titus 1:6), but polygamy itself is not forbidden. Polygamy was not God’s original intent (Genesis 2:24; Ephesians 5:22-33), but it was also something He allowed (see the examples of Jacob, David, and Solomon). The closest the Bible comes to forbidding polygamy is Deuteronomy 17:17, which is properly understood as God’s command against a king of Israel taking many wives. It cannot be understood as a command that no man can ever take more than one wife.
So, if a man has multiple wives and becomes a Christian, what is he supposed to do? If polygamy is illegal where he lives, he should do whatever is necessary to submit to the law (Romans 13:1-7), while still providing for his wives and children. If polygamy is legal, but he is convicted that it is wrong, he should divorce all but one wife, but, again, he must not neglect providing for all of them and their children. They are his responsibility. If polygamy is legal and he has no conviction against it, he can remain married to each of his wives, treating each one with love, dignity, and respect. A man who makes this decision would be barred from church leadership, but it cannot be said that he is in explicit violation of any command in Scripture.