I was just trying to point out the implications of his belief that "God and His word does not change" and showed that he don't really believe in that.
As for your 2nd point about the new covenant, if you are willing to understand Hebrews 8:8 as it is literally written, this is what you will conclude
For finding fault with them, he saith, Behold, the days come, saith the Lord, when I will make a new covenant with the house of Israel and with the house of Judah:
1) The new covenant promised by God is not here yet, it will be made in the future, in the age to come, when Israel as a nation finally accepts Jesus as their Messiah.
2) And even then, it will be made with the nation Israel, and not the Body of Christ.