Why is God going to judge the Gentile world system?
God will judge the Gentile world system because it rejects His offer of grace, His blessings, and believing who He is and what He is. Just as Israel experienced God's severity for rejecting so much after being offered so much, Gentiles are approaching the same place, and God will break them off.
Les explains that Paul warns Gentiles not to be high-minded but to fear. If God did not spare the natural branches, the good tree of Israel, then He will not spare the no-good tree. Israel experienced God's severity because they rejected so much after He had offered them so much. Now Gentiles are fast approaching that same place where God will finally get fed up with the Gentile world system, which rejects His offer of grace, His blessings, and believing who He is and what He is. God will do the same thing: He will break off the Gentile, and when He is through with the Gentile, He will put the Jew back. This demonstrates that God is not through with Israel; He will yet fulfill all the promises made to Abraham. In the interim, while Israel has been blinded, Gentiles were brought into the place of blessing.