Why did God raise up another apostle and send him to the Gentiles?

Les explains that after walking through the Old Testament, the Abrahamic Covenant, Christ's coming to Israel as Messiah, Israel's rejection of Him, and Israel's continued rejection in the early Acts period, God raised up this other apostle and sent him to the Gentiles with the Gospel of the grace of God. Les teaches that this is logical because there was no way to bring the whole Gentile world under Judaism, legalism, and the Law. Now that the work of the cross was completed and finished, God could pour out His grace on the whole human family, not just Israel. He also notes that in Acts chapter 2, God was still dealing with Israel, as Peter says, let all the house of Israel know assuredly that God hath made that same Jesus whom you crucified, Lord and Christ.