Genesis 18:12

Sarah laughed - Partly through pleasure at the bare idea of the possibility of the thing, and partly from a conviction that it was extremely improbable. She appears to have been in the same spirit, and to have had the same feelings of those who, unexpectedly hearing of something of great consequence to themselves, smile and say, "The news is too good to be true;", see Genesis 21:6. There is a case very similar to this mentioned Psalm 126:1, Psalm 126:2. On Abraham's laughing, See note on Genesis 17:17.

18:12 Sarah laughed within herself — It was not a laughter of faith, like Abraham's, Genesis 17:17, but a laughter of doubting and distrust. The great objection which Sarah could not get over was her age. I am waxed old, and past child-bearing in a course of nature, especially having been hitherto barren, and which magnifies the difficulty, My lord is old also. Observe here, That Sarah calls Abraham her lord, and the Holy Ghost takes notice of it to her honour, and recommends it to the imitation of all Christian wives, 1 Peter 3:6. Sarah obeyed Abraham calling him lord, in token of respect and subjection.