In An Open Letter to R.C. Sproul, John G. Reisinger, noted evangelist, author, and teacher of the Word of God for over fifty years, offers these observations:
A third change to the adultery commandment concerns polygamy. Under the Law of God given to Moses, polygamy was not considered adultery. In fact, the Law of Moses actually mandated that a man had to sleep with both wives if he took a second wife (Exodus 21:10, 11). I think any honest person will admit that a change from a law allowing, even if we make it a reluctant tolerance, polygamy to a law insisting on monogamy alone (Ephesians 5:22, 23) is more than just a surface change in the definition of adultery and marriage. John Murray clearly saw this problem, and because he was an extremely honest writer, frankly admitted what was at stake. He wrote his treatise on ethics attempting to prove that polygamy was just as sinful for David as it would be for us today. If that cannot be proven, and it surely cannot, then there are two canons of conduct, one for Israel and one for the Church, and Covenant Theology loses its foundation.