What did Israel's rejection of Christ accomplish in God's eternal purposes?
Israel's rejection of Christ as valid King/Redeemer fulfilled God's eternal purposes by bringing salvation to the whole human race apart from Israel, the Law, the Temple, and proselyting. It opened salvation by faith alone, so the blessing of Abraham could come to the Gentiles through Jesus Christ.
Les teaches that Christ came and presented Himself as the King of Israel, and it was a valid offer. He came to His own to be their Redeemer and King, but they rejected that offer. Rather than defeating God's plan, that rejection fulfilled the eternal purposes: salvation went to the whole human race without Israel, without the Law, without the Temple, and without proselyting. It became salvation by faith, and faith alone. Les adds that Christ became the curse, hung on a stake like Deuteronomy's wayward rebel son, so the blessing of Abraham might come on the Gentiles, not through the salvation of Israel, but through Jesus Christ. Les also says believers have reason to be happy and joyful, while avoiding both wild emotionalism and staid religionism.
That the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith.