Esau and Jacob are used as a symbol of the Jews and Gentiles.
Esau is the firstborn symbolizing the Jews, and Jacob is the second born symbolizing the Gentiles.
See
Genesis 25:23 And the LORD said unto her, T
wo nations are in thy womb, and two manner of people shall be separated from thy bowels; and
the one people shall be stronger than
the other people; and the elder shall serve the younger.
Paul is explaining how the plan for salvation was made BEFORE ANYTHING and ANYONE was born.
It means that the firstborn, according to the Jews who did the works of the law, is the first chosen, but God chose the second born for the salvation that saves.
The scriptures say that when Jesus came and made a new covenant based on faith, God cut off and hardened the Jews who didn't already have faith in Him, for some Jews had faith in Him and some did not, because the law was not based on faith. Those Jews were cut off and hardened so that they could not believe in Jesus at that time and be saved.
God cut off and hardened the Jews who did not already have faith when Jesus had his earthly ministry, and the Jews who already belonged to God by faith, they believed in Jesus, because they recognized what Jesus was saying as the words of God.
Jesus said when he is lifted up he would draw all to him, which means then all could come to him to be saved, the cut off Jews and the Gentiles.
Paul goes on to explain that some Jews might say why then does God blame us? And Paul explains not to question God, for God is wiser than us.
Paul also explains more and teaches how God bound all to disobedience so that He can have mercy on all.
See God hardening some of the Jews while Jesus had his earthly ministry is proof that Calvinism is false, for if God causes people supernaturally with the Holy Spirit to believe---then He wouldn't need to harden them.
Just like God hardening the Pharaoh, he was hardened to not believe...that disproves Calvin and Luther's teachings.
God hardened the Pharaoh as a punishment for what he did, and God hardened the Jews who did not have faith as punishment too, but not a lasting one, since they all could come to Jesus to get saved once Jesus was lifted up from the earth.