Romans 9:8-9 : 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. If it had been the children of the flesh, then all Abraham's sons would have been included in the promise. But Isaac was a child of prom-ise. Christians are now children of promise as much as was Isaac. How Isaac was. a child of promise is told in Romans 9:9.