Why did Israel lose the opportunity to be a kingdom of priests to the Gentiles?
Israel lost that opportunity when she rejected the Messiah. At Sinai, God had promised that if obedient, Israel would be a kingdom of priests, every Jew a go-between for the Gentiles and God. But when the nation fell and rejected Messiah, she also rejected that glorious prospect, so God turned directly to the Gentiles through Christ.
Les explains that Israel fell out of the picture when she fell. When she rejected the Messiah, she also rejected the opportunity of being a Kingdom of Priests to the Gentile world. He points back to Exodus 19, where God told Israel at Sinai that if they would be obedient, He would make of them a kingdom of priests. Every Jew could have been a go-between between the Gentile world and their God. But they blew it and dropped the ball. Yet God did not stop; now Paul can write that Gentiles receive the blessing of Abraham directly through the Lord Jesus Christ, not through Israel. They do not have to wait for Israel to get her act together or for a Jew to come to their community with the knowledge of God. God went straight to the pagan world with salvation without Israel as a go-between.
That the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith.