Why does God go back to the patriarchs when He deals with their offspring?
God returns to the patriarchs because of His love for them and because the gifts and calling of God are without repentance—meaning God does not change His mind. The remnant of Israel is beloved for the forefathers' sakes, Abraham, Isaac, Jacob, and Moses, as God continues His end-time purposes.
Les explains that God has to constantly go back to those patriarchs and His love for them when He deals with their offspring. Paul is saying that the election, the remnant of Israel, is still beloved because of their forefathers—Abraham, Isaac, Jacob, Moses, and so on. God is still preparing that remnant for the end-time events. In verse 29, the gifts and calling of God are without repentance, which means without changing His mind. God has not changed His mind when it comes to His dealing with Israel, and this all refers back to Genesis 12.