We read in the Bible that many of God’s people had two or more wives e.g. Abraham, Jacob, David etc. We should note, too, that in every one of these families there was much friction and unhappiness. Sometimes there was tension between the wives, as in the case of Abraham (Genesis 16,21). Sometimes the husband loved the one wife more than the other, like Jacob (Genesis 29:15-35). It also happened that the children of the different wives argued and fought, as in the case of David (2 Samuel 13). Therefore, it appears that marriage with more than one wife makes for a difficult situation. Why is this so?
To find the reason, we must go back to the institution, or beginning, of marriage (Genesis 2:18-24). In verse 18 God says very clearly “I will make a suitable companion to help him,” not two or three companions. His will is that two people, a man and a woman, should become one (verse 24). We find that in the New Testament, whenever marriage is spoken of, this verse is quoted. For instance, in Matthew 19:5-6, Jesus said “For this reason a man will leave his father and mother and unite with his wife, and the two will become one”.
It is possible for two people to belong together in such a way that they become one in ideals, planning and service for the Lord, etc., but for three people to do this is impossible. Therefore it is clear that, from the beginning God intended that one man should marry one wife and that they should become one.
For this reason, it is required in the Christian church that anyone who wishes to become a leader should have only one wife (1 Timothy 3:2, 12). No-one who has more than one wife may take responsibility in the church.
So to answer your question, we can answer that the Bible teaches clearly that a man may have only one wife.
If a person was married to two wives as an unbeliever, because tradition allowed it, and has since accepted Jesus as his Saviour, he will not be prevented from becomming a child of God. He will be accepted by God. John 1:12 says that those who receive Jesus and believe in him will be given the right to become God’s children. God will forgive all his sins, even those done in ignorance, (1 John 1:7, 9; Psalm 103:8-13).