Nahmanides says Avram “inadvertently committed a great sin…because of his fear of being killed. He should have trusted in God to save him, his wife, and all he had” (the other people with him)
Rabbi David Kimhi defends Avram, saying that he has to choose between two evils. By this subterfuge, Sarai may be violated, but at least they will both survive; otherwise he will die and she will be helpless in any case.
The Zohar has another view: Avram thought that Sarai had more spiritual merit than he had, so he didn’t fear for her but, only for himself. Why did Arvam think Sarai was his spiritual superior? Perhaps he saw a holy presence with her (and not with him).
Perhaps she was his superior because Sarai influenced many more people to become Jews than Avram did, as Rabbi Yohanan said: Avraham hindered people from coming under the wings of the Shechinah (becoming Jewish) and thus his descendants were punished in Egypt.
Rabbi Chelbo said “A man should always be careful to honor his wife; for the blessing in his house is only due to his wife.” The sage Rava would remind the people of his city, “Give honor to your wives so that you will be blessed with wealth!
My midrash contends that while in Babylonia, Abraham hesitated to marry Sarah because she was very beautiful, and he feared other men stronger, richer or more powerful than he was, would take Sarah away from him.
Sarah promised Abraham that even if kidnapped physically she would never be spiritually divorced from him. Whatever happened, they would grow together in love. Everything would turn out for the best if he always trusted God and his wife.
Sarah was an Ayshet Hayil — a woman of valor who didn’t worry about the time to come (Proverbs 31:25). Now his trust in Sarah and her promise was to be tested.
Rabbi Burton Visotzky takes another position: Avram does this less to “remain alive” than “that it may go well with me.” Visotzky asks: “Can we learn from Avraham who is deeply flawed yet nevertheless chosen? Why do we need saints and heroes so badly that we choose a very human Avraham as our model? Or is Avraham’s flawed humanity precisely the point?”