And God said, Sarah thy wife shall bear thee a son indeed,
&c.] This is repeated for the confirmation of it, and thus expressed to remove all doubt about it, if any there were, that hung upon Abraham's mind; as well as to let him know that the promise of a son by Sarah was not to be superseded by his prayer for Ishmael, for whom he might have a greater flow of natural affection than for his unborn son, in whom his seed should be called:
and thou shall call his name Isaac;
which signifies "laughter"; and which name was given him from the laughter of Abraham at the promise of him, and not from the laughter of Sarah, which as yet was not; wherefore Josephus F16 is wrong when he suggests, that Isaac had this name from Sarah's laughing at God's saying, that she should bear a son: though his birth was matter of laughter and joy to both, as it was to all good people that heard of it, ( Genesis 21:8 ) . So Polyhistor F17 from Melo, an Heathen writer, speaking of Abraham, says, that of his married or lawful wife one son was born to him, whose name in Greek is "Gelos", that is, laughter. Isaac is one of those the Jews F18 observe had his name given him before he was born, (See Gill on Genesis 16:11):
and I will establish my covenant with him, for an everlasting
covenant, [and] with his seed after him;
the covenant of circumcision just made with Abraham, the promise of the land of Canaan to him and his posterity, and of the Messiah that should spring from him, until whose coming this covenant would continue, and therefore called everlasting.
F16 Antiqu. l. 1. c. 12. sect. 2.
F17 Apud Euseb. Evangel. Praepar. l. 9. c. 19. p. 421.
F18 Pirke Eliezer, c. 32. Shalshalet Hakabala, fol. 2. 1.