The mother of one of my students recently emailed to ask for my thoughts on the question of why God allowed polygamy in the Old Testament, but prohibited it in the New Testament. (The question had come up in a Bible study.) It raised some interesting points having to do with the relationships between the Law and grace and between the Old and New Covenants, so I decided to post my response in edited form here as well.
When considering polygamy, it is important to begin by noting that permitting is different from sanctioning. God never specifically forbade the taking of multiple wives, but neither did He ever indicate that He approved of it. An obvious analogy is divorce, which was not forbidden in the Mosaic law, but which Jesus nonetheless condemned as wrong. “He said to them, ‘Because of your hardness of heart Moses permitted you to divorce your wives; but from the beginning it has not been this way. And I say to you, whoever divorces his wife, except for immorality, and marries another woman commits adultery'” (Matthew 19:8-9). Jesus says this despite the fact that Moses actually established rules for divorce in Deuteronomy 24:1-4.
As Jesus makes clear in Mark 10:2-9, when considering either polygamy or divorce the key principle is that, from the very beginning in the Garden, the model has been one man and one woman becoming one flesh. This principle didn’t change between Malachi and Matthew. Thus, we can assume that polygamy and divorce have never been right, and have in fact been wrong, throughout human existence. So why didn’t God outlaw these wrongs in the Law?
Answering this question requires consideration of the purpose of the Law. The Old Testament Law was never intended to make man righteous. “For if a law had been given which was able to impart life, then righteousness would indeed have been based on law. But the Scripture has shut up everyone under sin, so that the promise by faith in Jesus Christ might be given to those who believe.” The Law was a “tutor” that would “lead us to Christ, so that we may be justified by faith” (Galations 3). Even in the Old Testament, salvation came through faith in Christ, prefigured in the sacrificial system.
The purpose of the Law was to point us toward the Savior, not to provide an exhaustive catalogue of sin. It did not condemn every possible wrong action, and did not try to. Jesus confirmed that when he said that whoever hates his brother or lusts after a woman in his heart is guilty of sin (Matthew 5:21-28), even though the law did not specifically mention those actions as being sinful.
One could ask why God didn’t condemn polygamy, divorce, hatred, or lust in the law, but it seems clear why He didn’t intend the Law to list all possible sins. Human beings couldn’t even keep the Law as written, so adding additional forbidden behavior wouldn’t have helped us become any holier. It wasn’t the Law’s job to make humans holy or save them, even in the Old Testament.
Those who sinned in Old Testament times could only be saved through faith, whether they sinned by knowingly violating the written law or not (even today, every Christian does things that are actually sinful without being aware of it). If polygamy was forbidden in the Law, those who practiced it could only be forgiven through faith. If polygamy was not forbidden in the Law, those who practiced it could only be forgiven through faith. Since God can forgive unrecognized sin, the omission of a particular sin from the Law would not affect the possibility of salvation for those who unknowingly engaged in such sin. The question, instead, is whether inclusion of that particular sin would serve the tutorial purpose of the Law. Given polygamy’s exclusion from the Law’s prohibitions, it seems that question can be answered in the negative in its case. Presumably a similar explanation could be offered for divorce, hatred, lust, and other unlisted sins.
This does not mean that engaging in such sins would have been without consequence. Polygamy, for instance, is recorded as contributing to Solomon’s downfall (I Kings 11:4). Similarly, David’s lust for Bathsheba set in action a tragic domino effect that ended with the deaths of two innocents and a sharp chastening from the Lord (II Samuel 11-12). Neither Solomon nor David could plead ignorance, however. Even though neither polygamy nor lust were explicitly forbidden in the Law, warnings and counsel abounded. Not only did Solomon have the guidance of the “one man and one woman becoming one flesh” principle that recurs throughout Scripture, he also ignored the command in Deuteronomy 17:17 that the king “shall not multiply wives for himself, or else his heart will turn away.” And in David’s case, as Jesus pointed out in the New Testament, one who was truly seeking to please God would realize that fantasizing about the sin of adultery was hardly a recipe for spiritual health. Even when certain sins were not prohibited in the Law, the warnings were clear enough that those who indulged in them and suffered the consequences had only themselves to blame.
For the New Testament Christian, the situation has changed in several ways. It may appear odd at first glance that New Covenant freedom from the law would mean that sins such as polygamy, divorce, hatred, and lust are now impermissible in a way that they were not in Old Testament times, but in fact it makes perfect sense. The tutor is no longer needed to remind us of our need for a savior, but that is only because the Savior Himself has come – and that changes everything.
There is no standing still in the spiritual world. One is either moving toward God or away, and moving toward God means casting aside anything that separates us from Him, that is contrary to His character; anything that is wrong. And since we now have Christ working in us to do what we cannot by ourselves, it is possible to be holy in a way that was impossible under the law. Thus, even wrongs which were not prohibited by the Law must nonetheless be avoided by Christians today, because our goal is different. We are no longer seeking to follow a set of rules; now we seek to become like a person, the God-Man, with His help.
We must not practice polygamy, or divorce, or hate our brother, or lust in our heart, because doing so makes us less like our Lord. We aren’t breaking the Law (for the Law no longer needs to point to the Savior), but we are breaking our relationship with the Savior the Law pointed us toward. Of course, moral lapses can and will be forgiven graciously and repeatedly, but the one who knowingly chooses to walk in polygamy, or divorce, or hatred, or lust, or any other sin, is thereby choosing to walk away from his only hope of life.
The Old Covenant polygamist would face the consequences of his wrong in this life, but if he sought God in faith he could be forgiven for this unrecognized sin along with all others. In contrast, for those of the New Covenant some things which were merely dangerous three thousand years ago have become deadly, but only because we see with greater clarity and walk with nearer help.