That being said, the Bible strongly suggests that God’s intention for marriage was the monogamous union of one man with one woman. In the creation narrative of Genesis 2, God creates one man and one woman, saying: “Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh.”
In Deuteronomy, Moses warns future kings against acquiring many wives (17:17), and the book of I Kings notes that it was King Solomon’s love for many foreign women which led to his downfall (11:1-8).
Throughout the Old and New Testaments, marriage is used as an analogy of the relationship God and his people, personified as (one) woman. The analogy would lose its power if it were suggested that there could be numerous wives in the picture.
By the time of the New Testament, the question scarcely needed to be discussed. By the first century, Jews understood marriage as a monogamous relationship. Therefore, the gospels record Jesus dealing with a different problem: divorce. Jesus taught against the practice of divorcing one woman so that one could marry another one. According to Jesus, “Whoever divorces his wife and marries another commits adultery against her, and if she divorces her husband and marries another, she commits adultery” (Mark 10:11-12). If, therefore, it is considered adultery to divorce one and marry another, it follows that marrying another without divorcing the first has the same result.
Later, when Paul is writing to Timothy he specifies that overseers and deacons must be “men of one woman” or “husband of one wife.” It is not clear exactly what Paul meant. Although the Greek world had largely abandoned polygamy by that time, it may be that some in Ephesus still practiced it. Perhaps more likely, Paul is stressing that these church leaders should be faithful to their wives, not having extra-marital affairs or divorcing and remarrying.
If God intended monogamy, why didn’t he say anything about it in the Old Testament, when there were many ancient Israelites with multiple wives? The Bible is a record of God progressively revealing more and more of himself and his plan. Just as Abraham was not ready to hear everything that God would one day do through his offspring, the Hebrew people were not ready to hear all of the changes God would want in their lives (indeed, they had enough trouble learning to stop worshiping wooden idols).
Additionally, it might be noted that the early Hebrews were in a very different sociological context. The situation was not unlike tribal peoples of Africa in more recent times, in which there are frequent conflicts. Men go to war and are often killed, leaving a very high women-to-men ratio. For the survival of the tribe, men in such contexts take on more wives both to bear children to replace those who were lost, and to see to it that these women were cared for. When missionaries first arrived in Africa and saw the polygamy, some insisted that those who became Christians get rid of all wives but one. This caused an unfortunate amount of conflict, confusion and trouble; the missionaries did not understand that it would be tantamount to a death sentence for the abandoned women with no one to protect and feed them.