2072. 'And laughed' means the affection for truth. This becomes clear from the origin and essential nature of laughter. In origin it is nothing other than the affection for truth or the affection for falsity, which produces the mirth and pleasure exhibited in the face by means of laughter. This shows that the essential nature of laughter is nothing else. Actually laughter is something external belonging to the body since it belongs to the face; but in the Word interior things are expressed and are-meant by exterior. Just as all interior affections of both areas of mind (animus et mens) are expressed and meant by the face; interior hearing and obedience by the ear; internal sight, which is understanding, by the eye; power and strength by the hand and arm; and so on; so is the affection for truth expressed and meant by laughter.
 The principal element in man's rational is truth. Also present in the rational there is the affection for good, but this affection is present within the affection for truth, as the soul within it. The affection for good present within the rational does not express itself in laughter but in a type of joy and a resulting sense of delight which does not laugh. For laughter generally entails something that is not so good. The reason truth is the principal element in the rational man is that the rational is formed by means of cognitions of truth, for there is no other possible way in which anyone can become rational. Cognitions of good are truths just as much as cognitions of truth are truths.
 That 'laughter' here means the affection for truth becomes clear from the fact that this verse records Abraham's having laughed, as did Sarah both before Isaac was born and after, and also from the fact that he was given the name Isaac from 'laughter', for the word 'Isaac' means laughter. The fact that Abraham laughed when he heard about Isaac is clear from the present verse, for it is actually stated that when he heard about a son by Sarah he laughed. Sarah's laughing as well before the birth of Isaac when she heard from Jehovah that she was going to give birth is referred to as follows,
When Sarah heard at the tent door Sarah laughed within herself, saying, After I have grown old, shall I have the pleasure, and my lord being an old man? And Jehovah said to Abraham, Why did Sarah laugh, saying, Shall I in truth bear now I have grown old? Sarah denied it, saying, I did not laugh; for she was afraid. And He said, No, but you did laugh. Genesis 18:12-13, 15.
Also later on after Isaac's birth,
Abraham called the name of his son Isaac (laughter). Sarah said, God has made laughter for me; everyone hearing of it will laugh at me. Genesis 21:3, 6.
Unless 'laughing' and the name Isaac, which means laughter, embodied such things these occurrences would never have been mentioned.