Commentaries:
"The children of the promise are counted for the seed" means Abraham's seed, and "the children" are Esau and Jacob. Jacob was chosen or elected by God, but Esau was not. So through whom would God work? Obviously, it was Jacob, who on the surface was the weaker of the two—perhaps in character and certainly bodily. The question immediately arises, "Is it fair of God to do this?"
John W. Ritenbaugh
The Covenants, Grace, and Law (Part Eleven)
Other Forerunner Commentary entries containing Romans 9:8:
Genesis 35:10-11
Matthew 10:5-7
Luke 16:22
John 3:7
Galatians 4:24-26