One issue that is often brought up when discussing the Old Testament is the apparent approval of polygamy. There is no denying that the historical narratives of the Old Testament record great men of the faith, Abraham, Jacob, and David – just to name a few, as having multiple wives, but does the Bible approve of this action? To best answer this we will use the Word of God, and allow the Bible to interpret the Bible.
First, the Bible teaches that when God looked at His creation He said it was very good, (Genesis 1:30) and this creation consisted of one man and one woman (Genesis 1:27). Therefore, we know from Scripture that whatever the Lord creates is perfect, without blemish and should be considered a template of how things are to be done.
Second, when the Lord instituted the first marriage, He did so with one man and one woman. If the perfect or ideal marriage was for a man to have multiple wives it would seem that the first marriage, the template of marriage, would have demonstrated this (Genesis 2:24). In addition, in the New Testament when Jesus teaches on the subject of marriage He said,
“Have you not read that He who created them from the beginning made them male and female, ] and said, ‘For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh’?  So they are no longer two, but one flesh. What therefore God has joined together, let no man separate. – Matthew 19:4-6 (NASB)
If multiple wives were acceptable then Jesus would have taken the opportunity to teach this truth to His disciples.
Third, we must remember that the Bible records without error both the righteous deeds and the unrighteous deeds committed by individuals. Just because the Bible records an event or an action does not necessarily mean that the Lord endorses or approves of it, only that we can trust that the event or action took place. Therefore, just because the Bible records polygamy does not mean that God endorses polygamy.
Fourth, The Bible teaches that the first person to take a second wife was a descendant of the unrighteous line of Cain, not the godly line of Seth.(Genesis 4:17-24). In fact, the pagan practice of polygamy did not enter into the godly line of Seth for over 2,000 years (Abraham being the first).
Fifth, one argument that is often used to demonstrate that God approved of multiple wives in the Old Testament is that some of the men who took multiple wives were blessed by the Lord. It is often incorrectly assumed that this blessing equates to some type of approval. However, we know that this line of logic stems from not having a firm understanding of God’s Word. The Bible teaches,
for He causes His sun to rise on the evil and the good, and sends rain on the righteous and the unrighteous. - Matthew 5:45 (NASB)
Therefore, according to the Bible we cannot equate blessings with approval of actions. Furthermore, if we inspect our own lives we will see that the Lord chooses to bless us even though we have sin in our lives. If the Lord withheld blessings from His children until they were sinless, no one would receive any blessings.
We can clearly see from Scripture that the Lord’s plan for marriage is one man and one woman for a lifetime, and anything outside of this is a sin. While this is the Lord’s intent for marriage, we as humans have free will, and as such have the ability to accept the Lord’s perfect plan and version of marriage or reject His plan and accept an ungodly, pagan version of marriage.
Grace and Peace,