Paul has a concern that his Gentile readers will become proud of their inclusion in the family of God, in the covenant God made with Israel — as he said of Jews/Israel, and he is also concerned that this arrogance will lead to despising Israel. Not so, Paul says: If God lopped off the unbelieving Jew, he can do the same to the Gentile believer whose faith fails.
So Romans 11:17-24. Lots could be said here, but the big idea is clear: Gentiles should not get too comfortable with the God of Israel.

“If God did not spare the natural branches, perhaps he will not spare you” (11:21). And Paul lays the emphasis here on their need to continue in faith: “provided you continue in his kindness.”
Israel, he reminds them, may in the end turn back (11:23).
Wright contends that Paul has in mind not so much individuals but the Gentile church being lopped off. Why? Because of the assurance of Romans 8 (686).