Let's not confuse the promise to be heir of the world with God's covenant with Israel.
Consider Deuteronomy 18
17 The Lord said to me: What they say is good. 18 I will raise up for them a prophet like you from among their fellow Israelites, and I will put my words in his mouth. He will tell them everything I command him. 19 I myself will call to account anyone who does not listen to my words that the prophet speaks in my name.
(NIV)
How will God approach the Israelite who does not believe the Prophet, like unto Moses, the prophet named Yeshua. Will He say to them, you are no longer Israel, and therefore this passage does not apply to you. Does God only apply this passage to the church now, since the church is Israel?
No, God made a covenant with Israel, and if a Jew does not believe in Yeshua, God will hold Him to account.
Why would Paul have told the Galatians that if they were to be circumcised, they would take upon themselves the obligation to obey the whole law if the law had been abrogated and the covenant were not still in effect? Why would Romans still speak of Jews being judged by the law?
Fortunately for the nation of Israel, the Bible contains promises of God restoring the nation after they had sinned. According to Romans 11, we are in a time now where the Gentiles are being brought it. It was God's plan to include Gentiles, not just Israelis, in the body of Messiah. Through Israel's disobedience, Gentiles are coming in.
God is using us (I am of Gentile descent as far as I know) to provoke Israel to jealousy. Therefore, He still cares for Israel. One day, the blindness will be lifted from Israel, and God will provide salvation for that nation.
There is salvation in no other name but the name of Jesus (Iesous, Yeshua). No flesh shall be saved by the works of the law.
How do you explain what you are arguing in light of Romans 11.