For not all who are descended from Israel belong to Israel, and not all are children of Abraham because they are his offspring, but "Through Isaac shall your offspring be named”.
This means that it is not the ethnic children who are God’s people, but the children of the promise, who have faith in Him, who are counted as Abrahams descendants.
The seed of Abraham who received [the birthright inheritance] here are physical decedents.
God promised Abraham and Sarah a son/heir. The couple waited,
the days grew into weeks; weeks to months; months to years.
This couple now in old age, who lacked/lost faith in God to give an heir and tried
through the flesh. We cannot rush promises given from God in our own way.
Abraham made the serious mistake; he agreed to the adulterous relationship
with Hagar, Sarah’s [Egyptian handmaid/bondwoman] through the flesh.
Abraham still wanted Ishmael, Genesis 17:18, but God chose Isaac, his first
lawful son. Abraham gave all that he had unto Isaac (Genesis 25:5)
Isaac was born by promise, and by a miracle from God.
The promise, as confirmed to Isaac, Genesis 26:3-5 all these countries....
"not all are children of Abraham because they are his offspring"
Ishmael and Abraham’s other sons were rejected from the birthright.
but "Through Isaac shall your offspring be named”.
"But my covenant will I establish with Isaac …” .
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Being the first born of Isaac, Esau would have inherited the birthright, but
he sold his birthright blessing for a bowl of soup, so it went to Jacob/Israel.
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Reuben, the firstborn son of Jacob and Leah, was entitled to the birthright,
that included a double portion of the inheritance and leadership of the family.
However, his actions led to the forfeiture of these privileges. The primary reason
for this loss is recorded in Genesis 35:22,
“For not all who are descended from Israel belong to Israel”
Reuben, a descended of Israel, was rejected from the birthright inheritance.
Joseph, the favorite son of the patriarch Jacob, that his envious brothers
sold into slavery in Egypt, receives the birthright inheritance.
Just as All Jews are Israelites, but not all Israelites are Jews.
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1 Chronicles 5:2 (KJV) For Judah prevailed above his brethren,
and of him came the chief ruler; but the birthright was Joseph's.
Both the birthright and the scepter promises were re-promised by
the Eternal to Abraham and Isaac and to Jacob before splitting.
The Septer promise [I have never heard you mention],
was separated from the birthright promise.