That isn't the case for a Covenant.
Heb.8 is speaking to Israel (note the words Israel and Judah in Heb.8:8) and isn't referring to our present salvation.
What is 'old' and done away is the old Mosaic covenant.
The Bible is the Old and New Testament, not Old and New Covenant.
Um, no, sorry, not so much. You’re trying to triangulate to an absolute distinction because dispensationalism requires you to do so. I understand. I used to be a dispensationalist. That ended one day in the cafeteria at Moody Bible Institute, many years ago. I finally met a dispensationalist fellow student who was more extreme than I. He had deduced that no Scripture applied to the church at all, apart from Ephesians. His problem, and yours, is that the writers of the New Testament/Covenant break the separation rule over and over again. This puts demands for mental gymnastics on the dispensational reader that are impossible for any reasonable reader to sustain.
For example, you think that the reference in Hebrews 8 to Israel helps your cause, when in fact it does the opposite. Nothing could be stronger evidence that the New Covenant and the Christian church are one and the same than Hebrews 8-10, in which the Jeremiah New Covenant prophecy is unambiguously applied to the contemporary Christian church of the author (I believe Paul).
Lest you have trouble accepting this, let me point out another example:
Amos 9:11 “On that day I will raise up The tabernacle of David, which has fallen down, And repair its damages; I will raise up its ruins, And rebuild it as in the days of old;”
Is not the tabernacle of David clearly Israel?
Yet what of the fulfillment?
Acts 15:14-18 “Simon has declared how God at the first visited the Gentiles to take out of them a people for His name. [15] “And with this the words of the prophets agree, just as it is written: [16] ‘After this I will return And will rebuild the tabernacle of David, which has fallen down; I will rebuild its ruins, And I will set it up; [17] So that the rest of mankind may seek the LORD, Even all the Gentiles who are called by My name, Says the LORD who does all these things.’ [18] “Known to God from eternity are all His works.”
In the fulfillment, it could not be more clear that the entire contemporaneous church, Jew and gentile alike, are in view, that James and the men of the Jerusalem Council applied those words directly to themselves and to the Gentiles who were entering the church.
Thus fails the one device essential to your exposition, that any reference to Israel or anything distinctly Jewish automatically proves an impassible distinction in the intended audience. Each passage must be evaluated in its total context, both micro and macro, without superimposing a preconceived scheme of artificial categories, especially when the net effect of such theories is to separate Christians from so much Scripture intended for their use.
Peace,
SR