Why is the Gentiles' day of gospel blessing coming to a close?

Les teaches that Romans 11 makes plain, by inspiration, that God is not through with the nation of Israel. Israel has been set aside for the last 1900 and some years—without the temple, without a priesthood, without a sacrifice, and without a homeland until our generation. In the grafting process, Israel was removed and her branches broken off, while the Gentiles—Gentiledom—were placed over the root of father Abraham. Gentiles have been under the blessing of having the gospel and the opportunity for salvation, but Les explains that their day is fast coming to a close because they too have been walking it underfoot. God's grace and patience will one day soon run out, and He will go back and pick up where He left off with Israel. Paul writes this to believers in Romans 11:25, and in the age of grace those are predominantly Gentiles, though there are certainly some Jewish believers as well.