Who are the children of the flesh in Romans 9:8?
They are those descended from Ishmael and later from Esau. Though physically descended from Abraham, they are not counted as the children of God and are not in the line of the covenants; rather, the children of the promise are counted for the seed.
Les explains Romans 9:8 by identifying the children of the flesh as those from Ishmael and then later on from Esau. They are still children of Abraham, but they are not the children of God and are not in the line of the covenants. By contrast, the children of the promise are counted for the seed. He also notes that the word seed is the Greek word zera, used much like the English word sheep, always the same whether singular or plural.
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.