Verses 19-21 form God’s fifth and final speech.

God said, “No, …”: No is God’s response to Abraham’s plea that Ishmael be the heir to the promises. This may be translated indirectly as “I will not do it through Ishmael,” “It will not be Ishmael.” But Sarah your wife shall bear you a son: for bear you a son see the parallel expression “I will give you a son by her” in verse 16. The repeated emphasis on God’s choice of Sarah as the mother is featured in some translations; for instance, “No. Sarah only, your wife, will bear….”

And you shall call his name Isaac: Revised Standard Version and Good News Translation have footnotes explaining that the Hebrew form of Isaac means “he laughs.” This name connects with verse 17, in which Abraham laughed at the thought of having a child at his advanced age. Different explanations are given in 18.12 and 21.6, but each is based on the same wordplay. Translators should explain in a footnote the meaning of Isaac’s name, since it is so closely associated with laughter in chapters 17 and 18. However, if persons in a translator’s own situation are sometimes named “he laughs” or “laughter,” it will probably not be necessary to use such an explanatory note. See “Names in Genesis” in “Translating Genesis,” page 8.

I will establish my covenant with him is the same wording as in 6.18, where God established a covenant with Noah. See there. As an everlasting covenant for his descendants after him is as in verse 7, but now the reference is to Isaac.

Quoted with permission from Reyburn, William D. and Fry, Euan McG. A Handbook on Genesis. (UBS Helps for Translators). New York: UBS, 1997. For this and other handbooks for translators see here .