What is God's plan of salvation for the Gentiles based on?
It is based not on temple worship or keeping the Law, but on Christ's death, which paid the sin debt. After Israel was set aside, salvation came to the Gentiles through the free gospel of grace—faith plus nothing—without the nation of Israel, as Paul proclaimed to the Gentile world.
Les explains that God was not unfair when He turned from the Gentiles earlier, because He knew what those Gentiles would have done with His offer of salvation; they had trampled it underfoot for 2,000 years. He then dealt with one nation, Israel, intending to use them to go back to the Gentiles, but even the favored nation failed. Therefore God went to the Gentiles without the nation of Israel. This is what Paul trumpets: the Jew had the promises, rejected them, and God sent them into dispersion. Now He has turned to the Gentiles with a tremendous plan of salvation based not on temple worship, not on keeping the Law, but telling the world that when Christ died, He paid the sin debt. Because Israel was set aside, salvation has come to us Gentiles. Les also cautions that God is not all through with the Jew; He will still come back to them, and their fullness will bring even more riches.