Your OP objective is debunked because you're parsing scriptures that don't fit together.
Those scriptures fit perfectly it is called "sola scriptura testing" of all doctrine. You might like to try it.
The fact that you find this or that scripture to be "inconvenient" does not make it wrong or out of place. I think we can all agree on that.
Yes, It's a fact that Heb 8:1-6 is talking about Christ, but Heb 8:7-12 is a OT prophecy from Jer 31:34.
Heb 8:1-6 sets the context for Heb 8:7-12 just at the point when you apparently wish "it did not". It shows who the one speaking is - ... it is Christ.
How is that a problem for anyone but "you" in that case?.
=========================== As already seen in the OP
1 Now
the main point in what has been said is this:
we have such a high priest, who has taken His seat at the right hand of the throne of the Majesty in the heavens, 2 a minister in the sanctuary and in the true tabernacle, which the Lord set up, not man... 6 But now He (
Christ) has obtained a more excellent ministry, to the extent that He (
Christ) is also the mediator of a better covenant, which has been enacted on better promises.
A New Covenant
7 For if that first
covenant had been free of fault, no circumstances would have been sought for a second. 8 For in finding fault with the people, He (
Christ) says,
“Behold, days are coming, says the Lord (Christ),
When I (
Christ) will bring about a new covenant
With the house of Israel and the house of Judah,
9 Not like the covenant which I (
Christ) made with their fathers
On the day I (
Christ) took them by the hand
To bring them out of the land of Egypt;
For they did not continue in My covenant,
And I (
Christ) did not care about them, says the Lord (Christ).
10 For this is the covenant which I (
Christ) will make with the house of Israel
After those days, declares the Lord:
I (
Christ) will put My (
Christ) laws into their minds,
And write them on their hearts.
And I (
Christ) will be their God,
And they shall be My (
Christ) people.
11 And they will not teach, each one his fellow citizen,
And each one his brother, saying, ‘Know the Lord,’
For they will all know Me (
Christ),
From the least to the greatest of them.
12 For I (
Christ) will be merciful toward their wrongdoings,
And their sins I (
Christ) will no longer remember.”
===============================
So then the NEW Covenant of Jer 31:31-34 known to Jeremiah and his readers writes the LAW of God "on heart and mind". That includes the TEN according to Paul in Eph 6:2 having "
honor your father and mother as the first commandment WITH a promise". And even in the NT - "
Sin IS the transgression of the LAW" 1 John 3:4. Which means it is "still a sin" - to take God's name in vain (Ex 20:7) - even for born again Christians.