It seems Sarah hadn’t bothered to make it. As they eat, his visitors point out that Sarah is missing, “Where is your wife Sarah?” (Gen 18:9). Abraham responds, “There in the tent” (Gen 18:9). Sarah has not honored their guests. Amazingly, one of them responds by saying, “I will surely return to you about this time next year, and Sarah your wife will have a son” (Gen 18:10). God is showing great grace to Sarah.
