Answer:
I believe the true model in the Old Testament was one wife since Adam and Eve were joined together by God and became one flesh. Genesis 2:24 Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh.
However, a case can be argued (in the Old Testament) of Jacob or David or others that took more than one wife and it was not sinful. God did warn Solomon and David that taking more than one wife would turn them away from God because their desires would be for their wives and not God.
In any case, that was a time when God had commanded for the earth to be filled and many believe it was permitted at that time so that more children could be born, especially to those who could afford more than one wife and be able to provide for the children.
Regardless, the New Testament model is VERY clear, and here are just a few verses:
1 Timothy 3:2 A bishop then must be blameless, the husband of one wife, vigilant, sober, of good behavior, given to hospitality, apt to teach;
1 Timothy 3:12 Let the deacons be the husbands of one wife, ruling their children and their own houses well.
1 Timothy 5:9 Let not a widow be taken into the number under threescore years old, having been the wife of one man,
Ephesians 5:33 Nevertheless let every one of you in particular so love his wife even as himself; and the wife see that she reverence her husband.
For those who say it was ok because it was in the Bible, it was also ok for a false prophet or teacher of God’s word to be stoned to death…I wonder if they would want to put their words to this test. They might not be so boastful of “what was in the Bible” or what they thought were Biblical facts if they faced such scrutiny.
Bottom line is – people who only want to prove they are right take one or two verses in the Bible and quote them out of context (even the devil did this when tempting Christ). Those who love God and cherish His words look at what the entire Bible says, and it clearly shows the model for today is one wife.