Genesis 20:11 - Ellicott's Commentary On The Whole Bible

Surely the fear of God... — Abraham’s general condemnation of the people had some excuse in the widespread depravity of the nations in Canaan, but was nevertheless unjust. Even as regards these nations, they were not utterly corrupt (Genesis 15:16), and both in Egypt and in Gerar the standard of morality was higher than Abraham supposed. His difficulty was the result of his own imperfect faith; but the fact that this artifice was arranged between man and wife when starting on their long wanderings, proves that they rather over-rated than under-rated the risks that lay before them. The expedient was indeed a sorry one, and shows that Abraham’s faith was not yet that of a martyr; but it also shows that both of them felt that Abraham might have to save his life by a means almost as bad as death. And thus, after all, it was no common-place faith, but one as firm at root as it was sorely tried and exercised.