In this week’s Torah portion, as in the preceding parsha of Lech Lecha, Sarah is abducted by the ruler of the country, first in Egypt by Pharaoh, and now in Canaan by Avimelech. Although the two episodes differ in certain respects, they both illustrate Avraham and Sarah's sound moral judgment, as well as providing insight into the social and ethical realities of the ancient Near East.
In Egypt Avraham realized that his wife's beauty was in stark contrast to the unattractive Egyptian women. Assuming that she was his wife, the depraved Egyptians would likely kill him in order to take her. However, by telling them that she was his sister, they would offer him gifts in exchange for her. (In reality, Sarah was actually his niece and at that time a niece was often referred to as a sister. As a brother or uncle, he had the right to accept gifts and marry her off in those days, just as a father did.)
Although Avraham knew that she would almost certainly be violated against her will, telling them the truth would have resulted in his death and her violation anyway. Therefore he elected to stall for time and drag out the negotiations, hoping for Divine deliverance.
In Parshat Vayera they are faced with essentially the same dilemma. He again refers to Sarah as his sister, and again
Avimelech, however, allowed them to stay in order to dramatically demonstrate that he had not defiled her. Avraham recognized that Avimelech was morally superior to Pharaoh when he says that his main concern was not Avimelech's immorality but rather, "Surely there is no fear of
Finally, Avimelech gives Avraham a gift of silver and says to Avraham enigmatically, "Let it be for you an eye-covering to all who are with you; and to all you will be vindicated." Avimelech was giving him advice: Use this money to purchase face-covering clothing worn by the undefiled modest women of that time. This will clearly indicate that she has been completely vindicated. Additionally, Avimelech is telling him that in order not to arouse suspicion in the eyes of everyone in the future, he should refrain from calling her his sister so that she will not be in need of miraculous intervention.