Adam Clarke's Commentary on the Bible - Genesis 18:13
And the Lord (Jehovah) said, etc. - So it appears that one of those three persons was Jehovah, and as this name is never given to any created being, consequently the ever-blessed God is intended; and as he was never seen in any bodily shape, consequently the great Angel of the covenant, Jesus Christ, must be meant. See note on Genesis 16:7 . read more
Adam Clarke's Commentary on the Bible - 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... read more