MODERATION AND PASSIONLESSNESS.
The apostle saw in these women the type of the two covenants, in accordance with the rule of allegory, but since what the text narrates actually took place, the literal sense also deserves consideration. The saints entered the married life not to pursue pleasure but for the sake of children. There is in fact a tradition that says they would go with their wives only when the time was suitable for conception. They would not go with them during the lactation period, when they were nursing their young, or when they were with child, because they regarded neither of these times as suitable for coming together. . . .
When Sarah, therefore, who was wise and holy, had observed for a long time that in spite of coming together with her husband she was not conceiving, she abstained from conjugal relations, and since she knew that it was in the order of things that he should have children, she gave him her slave girl as a concubine. This shows the moderation (sophrosyne) and the absence of jealousy of Sarah and the passionlessness (apatheia) of Abraham, who chose this solution at his wife’s instigation and not on his own initiative and who yielded to her request only in order to give birth to children. The literal sense too, then, is useful according to the considerations offered above.
On Genesis 235