Romans 9:7 and not all are children of Abraham because they are his offspring, but “Through Isaac shall your offspring be named.” (8) This means that it is not the children of the flesh who are the children of God, but the children of the promise are counted as offspring.
It is not the physical children of Abraham who are the children of God, but the children of the promise. Jesus Christ was the unique offspring that fulfilled the promise of an everlasting covenant between God and his spiritual people, and it was through the physical line of Isaac that Jesus Christ was born. All who are in Christ through faith are the spiritual children of Abraham and are the children of the promise. They are the sons of God and the recipients of the covenant promise of Genesis 17:7-8. God has never made any spiritual covenant or promise with Abraham’s physical descendents, Israel or any other group based on their ethnicity or birthright. Paul makes that very clear in this passage.
Focus on Christ #137