Genesis 18:15 - Ellicott's Commentary On The Whole Bible

Sarah denied. — With strange inconsistency Sarah knows that the speaker is Divine, and that He perceived the thoughts that passed “within herself” in the retirement of the tent, and yet denies; but it was the inconsistency of fright. Struck with terror at the thought that she had ridiculed the promise of Jehovah, she offers no excuse, but takes refuge, as frightened people are apt to do, in falsehood. Gently reproved, the result was the building-up of her faith, just as Mary’s doubt was removed and her faith perfected by the angel’s words (Luke 1:34-37).