Question: How do Preterist preclude Jeremiah 31 and the like "and my covenant with Zion is forever."
Answer: Many dispensationalists have in mind the following scenario.
1.) The New Covenant was to be made with Judah and Israel.
2.) God did not make the New Covenant with Judah and Israel because of Israel’s rejection of the kingdom. The kingdom, and thus the New Covenant, was postponed. The New Covenant will only be made with Israel when she is restored in the millennium.
3.) Since the kingdom is postponed, the church has temporarily replaced Israel, and the current gospel of grace (unforeseen and unpredicted in the O. T.) is in place until the rapture.
The problem with this scenario is many fold:
1.) The New Testament writers, with the exception of Luke, were all Jews and say that what was happening in their generation was the fulfillment of God’s promises to Israel (1 Peter 1:9-12).
2.) The New Testament writers speak in many places of the New Covenant as a reality (2 Corinthians 3 especially), and it must be kept in mind that Paul preached nothing but the hope of Israel. Thus, for Paul to affirm that he preached nothing but the hope of Israel, and he preached the New Covenant, can mean only that he preached and believed that the New Covenant promised in the O. T. to Israel, was being delivered.
3.) The writer of Hebrews 8 appeals directly to Jeremiah and the promise of the New Covenant, and says that the New, which was to offer forgiveness, was present. The millennialists have to deny what the text says to deny that the promised New Covenant was not being delivered.
4.) Every single thing that was to be present in the promised New Covenant is present in the New Covenant of Christ, i.e. the New Law is present in the heart, and it genuinely brings forgiveness of sin. What more could another New Covenant bring that the gospel does not bring?
5.) The gospel will never pass away (Matthew 24:35. So, if God makes another New Covenant, what happens to the gospel? See my article "The New Covenant" on the website. I am currently working on a small book on the New Covenant, that addresses the issue in depth. This is a critical issue since the millennialists insist that in the millennium animal sacrifices will be restored.
The problem is that the gospel of Christ abolishes animal sacrifices. So, if animal sacrifices are abolished by the gospel, exactly how will another New Covenant make animal sacrifices mandatory, without nullifying the gospel?
6.) Notice that God’s New Covenant would be in "Zion." Notice now that in Hebrews 12:18f the writer affirms "you have come to Mt. Zion!" To a Jewish reader, this would have been one of the most significant, exciting statements possible! Virtually all of God’s eschatological, and stereological promises were focused in Zion! (See my recent articles on the site as well, Zion the Perfection of Beauty). For the Hebrews writer to affirm that the first century saints had now come to Zion is a positive affirmation that the fulfillment of their hopes was on the verge of fulfillment. This is an incredible statement that is often ignored by dispensational commentators.