But I will establish my covenant with Isaac: But (used by both Revised Standard Version and Good News Translation) is a suitable transition in this context, in which the statement regarding Isaac contrasts with what has been said about Ishmael. In some languages the contrast will be naturally expressed in two statements, one negative and the other positive: “But I will not … with him; I will … with Isaac.” In other languages the force of the contrast may be brought out by the use of a word like “only”: “But my covenant I will establish only with Isaac” or “But that promise—I’m going to keep it with your own son Isaac.” For establish my covenant see verse 19.

Whom Sarah shall bear to you at this season next year: season probably should be taken to mean “about this time” in the sense of an appointed time rather than one of the annual seasons. In some languages this sentence may be more naturally expressed as in Good News Translation “who will be born to Sarah….”

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 .