Why does Paul switch from teaching Gentiles to talking about Israel in Romans 9?
Paul shifts to Israel in Romans 9 because of his deep love and continual sorrow for the Jewish people, wishing himself accursed for their sake. This parenthetical section addresses Israel's past, present, and future, after completing instructions and doctrines for Gentiles.
Les explains that this is a parenthetical section of Romans where Paul leaves off his instructions and doctrines for Gentiles and deals with the nation of Israel for three chapters—past, present, and future. Paul expresses great heaviness and continual sorrow in his heart for Israel, even saying he could wish himself accursed from Christ for their sake, because of his love for the Jew. Les compares this to Moses, who asked God to blot his name out of the book of life to spare Israel.