Romans 9:7-9

Amplified Bible, Classic Edition

⁷ And they are not all the children of Abraham because they are by blood his descendants. No, [the promise was] Your descendants will be called and counted through the line of Isaac [though Abraham had an older son].^(A)

⁸ That is to say, it is not the children of the body [of Abraham] who are made God’s children, but it is the offspring to whom the promise applies that shall be counted [as Abraham’s true] descendants.

⁹ For this is what the promise said, About this time [next year] will I return and Sarah shall have a son.^(B)