Why does Paul think all descendants of Abraham are Israel? ~ Cross reference of Romans 9:7 to Genesis 21:12,Genesis 18:10, Genesis 18:14
G-d made a promise to Abraham that his descendants will posses the land of Cannan and that G-d will multiply his seed. G-d later makes the same promise to Isaac that through his see the promise made to Abraham will be fulfilled. Finally G-d makes the same promise to Jacob that his name is Israel and his 12 sons will be blessed and the promise G-d made to Abraham, Isaac & Jacob will be fulfilled in them. So Paul stating that all dependents of Abraham are not Israel is correct. Ishmael, other sons through Ketura[Zimran, Jokshan, Medan, Midian, Jishbak, Shuah] & Esau[Isaacs's first born] are not Israel. As you go through the rest of Romans 9 you will see that Paul is using this statement that "All children of Abraham are not Israel, but the ones that came through faith [Isaac]" to later say that through faith the gentiles [Christians] by faith in the blood of Jesus are also Israel. Click to read how G-d established his covenant with Abraham to be called his ...