Healing His Patients Slowly
Recently, I preached on the devastating consequences of Jacob’s polygamous and incestuous marriage to Leah and Rachel. This was not the first time the Old Testament confronts us with the sticky problem of polygamy. It first appears in the genealogical record of Cain’s reprobate descendants, where we read of Lamech’s polygamous marriage and subsequent boastful defense of his murderous aggression (Gen. 4:19-24). We also read about Abraham’s relationship with Sarah and Hagar. We see the problem of polygamy unravelled in the narratives of other godly saints in the Old Testament. If the creation account in Genesis 1-2, the teaching of Malachi 2:15, and the clear testimony of the New Testament is that marriage is to be between one man and one woman, what are we to make of the fact that the patriarchal narratives seem to teach that God tolerated polygamy in the Old Testament?
In his Christian Theistic Ethics, Cornelius Van Til sought to explain Old Testament redemptive-ethical concessions by means of the analogy of a sick child who was not able to receive, all at once, all the medicine that he needed in order to live. He wrote,
"The case of polygyny being tolerated in the Old Testament is the classic illustration of the supposed low type of Old Testament ethics. Yet…Jesus himself interprets this as a pedagogical measure on the part of God in order to lead Israel on to the absolute ideal. It was for the hardness of man’s heart, and for the blindness of man’s eyes that God was willing to come down so low as to tolerate for a time that which is ideally out of accord with the absolute standard, so long as it was a stepping stone toward the absolute ideal. God frequently set the absoluteness of the ideal before men very vigorously. And that might lead us to ask why he did not do this consistently and at once set up the absolute ideal along the whole front of the ethical life...
The answer to this, we believe, must be found in the analogy of the convalescent child. The convalescent child needs strong medicine in order to live. It may need many varieties of strong medicine. But if these were all administered at once the child would die. So too if God had maintained the absolute standard at once along the whole front of the ethical life, we can see that he would not have attained his purpose. It was the all-wise physician who was healing his patient slowly, and giving him just the medicine that he could bear, and no more...
A child that is sick is not sick because of any special sins of its own. Yet the race is sick because of its own sins, and for no other reason. It is therefore only partially true to say that the lower demands of Old Testament ethics are due to the fact that God adjusts his demands to the times. That God makes concessions to low ethical practice is not in the least an admission that he has not the right to demand the fulfillment of the absolute ethical ideal." 
Van Til explained that he was relying on William Benton Greene’s treatment of the subject in Greene’s 1929 Princeton Theological Review article, “Ethics of the Old Testament.” Greene wrote,
“The sanctity of marriage ought to be insisted on always and everywhere. Nor is this done less emphatically in the Old Testament than in the New. The form, however, in the two is different. In the New Testament monogamy is invariably required. Men had then been developed up to an appreciation of this as the perfect relation. In the Old Testament a regulated polygamy was at times sanctioned. Men were not able then to bear the higher teaching of the New Testament on this subject. Nor would they ever have been able to bear it, had it been imposed on them without exception from the beginning. The claims of right must be urged gradually as men develop, if they are to be developed so as to meet its claims fully. Things being as they are, it would be the destruction of practical morality, were the right to be insisted on from the first in all its spirituality, or even, as we have seen, in all its comprehensiveness.”
Though this may not solve all of the difficulties in our minds, it certainly offers a plausible explanation for the fact that God–at times–made ethical concessions for pedagogical purposes in the Old Testament. The same principle holds true for why God tolerated divorce, despite the clear ethic of creation and the timeless ethic throughout redemptive-history. As Jesus said to the Pharisees, “Because of your hardness of heart Moses allowed you to divorce your wives, but from the beginning it was not so” (Matt. 19:8).
We must be clear that a concession is not the same as permission–neither is it the ethical ideal to which God holds us.
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1. Cornelius Van Til, Christian Theistic Ethics (The Presbyterian and Reformed Publishing Company: Phillipsburg, NJ, 1980).
2. William Benton Greene, “Ethics of the Old Testament," in Princeton Theological Review, XXVIII (1929), p. 190.