Charles Spurgeon Commentary Romans 9:8-10

"That is, it is not the children of the flesh that are children of God; but the children of the promise are reckoned for a seed. For this is a word of promise, According to this season will I come, and Sarah shall have a son. And not only so; but Rebecca also having conceived by one, [even] by our father Isaac--" — Romans 9:8-10 (ASV)

That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed. For this is the word of promise, At this time will I come, and Sarah shall have a son. And not only this; but when Rebecca also had conceived by one, even by our father Isaac; (Romans 9:8–10)—

When there were twins to be born of her—