Jamieson, Fausset and Brown on Genesis 12:11-13

11-13. Sarai's complexion, coming from a mountainous country, would be fresh and fair compared with the faces of Egyptian women which were sallow. The counsel of Abram to her was true in words, but it was a deception, intended to give an impression that she was no more than his sister. His conduct was culpable and inconsistent with his character as a servant of God: it showed a reliance on worldly policy more than a trust in the promise; and he not only sinned himself, but tempted Sarai to sin also.